Well Bob, your #1 problem is of course that they are trying to sell the idea of super hero cotinuity movies still. They have succeeded at it all of once, despite all odds, and did it largely by using some of the longest running, best known characters out there, and a basic plotline taken directly from the comics.
Pretty much every one of the characters you mention is the result of what is at best a moderate success at intentionally creating minority characters for the sake of having minority characters. In the case of most of them, such as Luke Cage, they have been accused of being offensive racial stereotypes and problem characters, as much as they have been embraced by the community at large. It's the time old issue that if you create a black (or other minority) character and they just act like a normal super hero, they get called a "minority by technicality". The recurring jokes by members of the group in question being that they never knew the ethnicity of the character based on behavior. On the flip side if they have the character act like a member of that ethnicity it becomes offensive on some level, either as some kind of oftentimes misinformed backlash empowerment fantasy, or just a flat out racial stereotype.
To "pick on" Cage for example, look at the "Civil War" event from years ago, people make a big deal about Luke Cage being involved, but was it because people actualy liked the character, or because of a PC stunt with Marvel wanting to put one of the only black characters they had at the forefront. A lot of what Cage did has become the stuff of fan parody. For example, early on when Marvel started to lose it's way with this being a "gray" issue and deciding to make it clearly black and white, and a modern political analogy, they had a thing with Tony Stark trying to recruit Luke Cage, and Luke Cage going off on Iron Man in making it all some giant analogy to slavery, including properly shocked reactions from Iron Man. This for a while lead to a few parodies of that scene with captions about how the man (Luke) just doesn't get the issue, or is stupid and gets angry about slavery because that's what Black men quintessentially do when confronted by any social issue they don't happen to like. A point not so much made by white people, but largely fueled it seemed by blacks who felt that this was both stupid, stereotypical, and out of context to that actual universe.... and really, this isn't the first time Cage has come to the forefront for garbage like this. As I've mentioned before Seanbaby once made a crack about how he had trouble reading "Power Man" because he was never sure if Luke wanted to beat someone up or dance with them due to all the jive he used (this was vintage). While exagerrated for humor, he has a point, and it's a funny way of pointing out the issue of him being a racial stereotype.
This isn't really about Power Man though, it's about practicality and how many of those characters are going to put butts in seats at this early stage. Sure, if this kind of crossover thing is still going on in 10 years or so, and becomes a staple, we can start seeing a lot of lesser characters and experimentation, but right now they are wise to work with the wll known characters and establishing the core. Pointing out that they are all white is just rabble rousing, and if they decided to start listening to that and changing things around due to politics, this whole experiment could die a crib death.
I'm also going to say rather cynically that the reason why The Avengers has had such a diverse roster is not because it's some kind of great politically correct thing that worked, and was intended to be diverse as some kind of message, but because it's Marvel's dumping ground. Typically The Avengers has one, or maybe two big heroes that carry their own weight popularity wise to act as a core, and otherwise is used as a place to stick characters who have some popularity, or a reason to exist, but can't hold a title on their own. Characters typically go to The Avengers in hopes that they will recover, or "hit" with some interest, and either do, or wind up gradually disappearing, to perhaps be revived later as a surprise, or make occasional apperances in other books. A lot of those female, and minority super heroes, kind of wound up being in "The Avengers" not because they made "the big leagues" but because they kind of sucked and this was their last chance to get some interest. For a lot of characters Avengers membership is basically a stop along the path to the graveyard. There ARE exceptions to this of course (like there are to anything, especially in comics), but saying "this guy was an Avenger", or pointing out that a character has bounced in and out of the Avengers does not typically mean good things. It typically means that for whatever reason Marvel is keeping a character on life support and doesn't want it to die for whatever reason, or present an avenue (called from Avengers reserves) to eventually revive a character they feel they need to retire, but think might hit later given the right events to use it.
The Avengers is not the JLA, where you pretty much get all the big, iconic characters togerther with great frequency, and also have the also rans. While people compare them,
their purpose and how they are used is a bit differant. Typically when The Avengers gets all of the major iconic characters together, they don't stay together all that long as they all have their own successful comic series to hold down, and in many cases sell better in their solo titltes (with regular crossovers) doing their own things in their own sphere. DC also has the JLA characters holding their own titles, but by trying to handle that is also infamous for making massive messes out of their continuity, and tons of contridictions because of it. Marvel is hardly "clean" here but it does tend to do things better and keep track of where characters are supposed to be at any time. DC has tried to deal with their interests by doing things in the past like creating dozens of alternate universes and versions of the characters who exist seperatly so they can write stories without worrying about all the other stories, needless to say that kind of thing got confusing fast. As a result DC frequently feels the need to reboot their entire continuity a lot more than Marvel does, not only do the Reboots sell a lot of comics (how will it happen this time?) but let's the deal with a writing style where things cease to make sense where one comic might contridict another entirely on how something works, and even occasionally where the same character might basically be written in differant places at the same time accross titles, and well... yeah, listing all of DCs antics and why they have needed to reboot would get crazy, it's not typically just one reason. The differance in styles accounts for a lot. Despite the hype, The Avengers doesn't tend to operate as an all star showcase that often... yet for the movies at this point it's kind of what they need to do, because they don't currently have the install base where people are going to pay to see a constant roster of minor and also ran heroes, B listers, former A listers, and new experimental creations.
You have to be a pretty serious comics nerd to know who Iron Fist, or Spider Woman actually are never mind what they can do or anything about them to see them in a movie. The amusement involved in the whole Spider Man/Woman confusion example is something that would really only appeal to the most extreme kinds of nerds (like me). If you actually know who Misty Knight and would like to see her in a movie, your by definition the kind of nerd, most other nerds are scared of. That doesn't mean there is anything wrong with her, or by association Iron Fist (there isn't, they are fine characters) but my god, that is so out of context to what your going to try and do in a movie right now it's kind of funny. It's like me saying I want a "Darkhawk" movie, or them to put "Blink" into something, or explore the concept of "X-man" in the X-men (or hey have the X-men fight Adversary, or do the Inferno storyline). Those are all things I'd like to see, without any political elements involved, but now isn't the time if it was ever going to happen even if I could make some kind of "outside" justification for any of it (diversity, etc..) because we're just not ready for that kind of fringe stuff in Hollywood, they have just now managed to finally after many attempts, managed to get super heroes to hit, and haves successfully made the first comics continuity movie. Keep the current characters/formula going for a while and establish itself before you start tossing wierd stuff in.
That said, I agree "War Machine" being used might not be bad, though there is an issue of redundancy with Iron Man (having to do twice as many armor FX and fight scenes, and show the same basic stuff, while still giving all the other characters their time) but that could be resolved. Pepper Potts is Tony Stark's girl friday... I see no real issue with the way they are handling that character.
