My quick, very verbose and long-winded quadruple-hay-penny.*
In a bow-flex commercial, you will only see well-toned, heavily exercised men and attractive, well-toned ladies in thin, revealing work-out clothes. In a job-opening-advertisement, you will only see happy, multi-cultural diverse workers doing their job in picturesque settings with determination, and the ability to solve all problems happily, hastily, and without failure or issue. In textbooks, you will find situations with enough information to adequately solve all of the problems, or discussions that are well-researched and thought out based on the subject it is speaking on.
In books, you will find flawed heroes and perfect villains. In movies, you'll find minority individuals being suppressed by majority figureheads, and in games, you'll see attractive women doing more while wearing less.
It's a stereotype, pure and simple. That's it, a shallow, silly, over-marketed and under-developed stereotype. Alas, here we are discussing it as if it really matters in the grand scheme of things. Let's look at life from an unbiased standpoint, that of the marketing crews.
Does Ivy or Taki's appearance affect a majority of the girl gamers at a strong enough point to stop them from buying the game. Answer majority, "No." Does marketing mostly-naked women on the cover of pre-teen, male-dominant (not male-centric, male-dominant) style game get buyers out of users who would previously be uninterested? Answer majority, "Yes."
You're getting mad at Game Devs for what Concept Artists and Marketing Execs decide. Instead, you're looking at it from the wrong perspective. Count a game on the gameplay's merit, then you can be happy with the game devs.
Now let's look at the numerous games that have simple, believable female characters as leads or majors. Star Wars: KotOR, Star Wars: KotOR II, Mass Effect, Perfect Dark, Perfect Dark: Zero, Orange Box's Portal, Metroid through Metroid Prime 3: Corruption, Donkey Kong Country 2, Seiken Densetsu III, Resident Evil, Later Pokemon Games, Super Princess Peach, Xenosaga, Jade Empire, Command and Conquer series, American McGee's Alice.
Just to name a few. And I could probably name more if I hadn't restricted myself to best sellers [http://en.wikipedia.org/wiki/List_of_best-selling_video_games].
Frankly, the stereotype exists because it doesn't annoy girl gamers enough to upset the market by continuing to do so. And as long as that works, then the market will continue as-is. Don't fix what isn't broken, after all.
That's all from me, frankly, these kind of discussions irritate me. You're calling on an entire community being at fault for something that businesses do that are both functional and profiting. Now, if you'd to fault the entire human race for driving regularly, or smokers for pandering to the life-killing business that push their own products...
Honestly, what do discussions of this do aside from alienate your fellow gamers by claiming them at fault for the games they play. The bottom line is this: Gamers like game that are fun, whether or not the females are tepid, attractive, giggly, or stereotypical. Calling us out on our hobbies is not a good way to garner support, instead, it's a great way to alienate your peers.
*[sup]This is based on the first post, as I have not read anything else in this thread. If I repeat points, or discredit others, it's entirely accidental. That is all.[/sup]