Let's consider offensiveness for a moment. First, grab a globe. Or call up a good world map, if you don't have one. Now, as many people above me have noted, offensiveness is both subjective and involuntary. A remark is not 'offensive' or 'inoffensive'; it simply is. I (or you, or whoever) am the one who is offended, or finds said remark offensive. Regardless of how it was intended, offense is in the eye of the recipient, not the creator. Of course, intent still plays a large part. What do I mean? Take a look at the globe. Turn it to Asia. Note how freakishly large Asia is. Consider the relative tininess of the portion controlled by the people commonly identified as 'Asian'. Arabs, Israelis, Russians, Persians, Turks, Khazaks, Indians- all these people are Asians- ethnically as well as geographically. By assigning the term 'Asian' to only a small subset of the people who it can be rightfully applied to, we're engaging in behavior that many would call offensive. I certainly would- but I don't, since I realize it's just the result of cultural-linguistic conditioning; there's no bad intent behind it.
The term 'Asian' is used because 'Oriental' has been deemed offensive. 'Oriental' simply means 'eastern'; less accurate, but also less inaccurate, and fallen from favor because of its association with horrifically racist actions and attitudes of the past. Likewise, the word 'Jap' (a shortened form of Japanese) is much more offensive than 'Brit' (short for British), despite 1. both words being formed the same way and 2. 'Jap' being more technically accurate; the Anglo-Norse-Norman inhabitants of the UK today being so far removed from the Celtic British the equivalent would be calling all US citizens 'Cherokee'. Surface level? Offensive. Derived intent? Blatantly not. In the previous paragraph, I referred to countries 'controlled by' a specific racial subset of people; most of you reading this read through that and figured I meant 'occupied by a permanent or semi-permanent population consisting primarily if not exclusively of' or some such; others assumed I was implying something rather more sinister; such as that the sneaky Thai people are scheming and plotting to secretly control the world, or perhaps that the sneaky yet stupid Japanese people are somehow scheming and plotting to secretly control Japan.
For you see, many people these days, especially but not exclusively on the internet, go about looking for reasons to be offended; in part because anger at someone else keeps them from having to address their own flaws, and in part because they suffer from a lack of passion in their own lives and seek to remedy that any way they can. Recreational outrage is a tragically common thing, damaging to both the people who engage in it and the society that they live in; but no less common for that. Making this more complex is that something can be inherently discriminatory, but not inherently offensive. Gender-segregated bathrooms are technically sexist; very few people consider them offensive. Racially segregated bathrooms are a different matter, and this brings us back to your other question.
I, for one, have never had a problem relating to people who are nothing like me. Consider the Transformers. Optimus Prime was a forty foot tall, five million year-old alien robot, thrust into a position of leading what was essentially an entire species permanently at war with another one, despite his prior life experience consisting of little more than being a dockworker. Desperate for energy sources, he leads a mission to another planet, but the ship gets attacked and ends up crashing into still another planet. Everyone on board is functionally (they're robots, remember) knocked unconscious, until the volcano erupts four million years later and reactivates the computer, which revives everyone. The planet turns out to Earth in 1985, and Prime now has to not only lead his forces continue the search for energy here, but still assume leadership of the war he thought he'd escaped and deal with the humans and the fact that he unleashed a horde of hostile, energy-demanding giant alien robots. I was an unusual four year-old, but I had never done anything like any of that, yet I had absolutely no problem relating to him. Neither did anyone else I knew who watched the show.
People are most comfortable with- and thus, most willing to spend money on- those who they think they'll be able to relate to, which often means people like them. Referring again to the Transformers, the idea of a society of artificial beings who rebelled against and overthrew their creators, existed for a long period in a state of perpetual war, then escaped to Earth, poses a lot of interesting questions- what is the art and culture of such a society like? Their philosophies? Religions? How are they going to interact with organic beings? Are the differences between a flash-in-the-pan 80 year lifespan and an I-live-as-long-as-I-want multimillion year one so great that the only way these meatsack insects can be seen to have meaning is by indoctrinating your robots with an all-consuming overriding philosophical ideology? Is Optimus Prime actually some sort of weird Christo-Buddhist zealot? I, and I suspect many of you, find these questions fascinating; part of being a gamer is immersing yourself in strange new worlds and exploring them. But many people find the idea exhausting, rather than invigorating. Sure, it might be kind of interesting, but to break so many points of contact with the familiar is draining; better to only go a bit at a time, and stick with what we're familiar with. Thus, when we got a (mostly) live-action movie in 2007, it was primarily about the humans who the interesting characters were dealing with- after all, who can relate to a robot?
To tie a post that is already rather long together: the problem with this comes especially true with black people. Within this country, and to varying extents this superculture, black people have had an abysmal time of it. Many of them have gone on to do quite well, it's true, but most of them are going to face difficulties others don't. The reasons for this are myriad, complex, and contested; suffice to say for now that one of the problems is a lack of (though I hesitate to use the term) suitable black role models in media; for a very long time, low-life was as high as it got. That has changed, though many would argue not enough. Once change started happening on that front, the other racial groups (or rather, advocates for them) moved in: some no doubt thinking 'hey, it would be cool to see a wider range of people', but all too many thinking 'this station's programming doesn't feature a single transexual lesbian Sino-Hispanic character! HOW DARE THEY?'. Look at from a distance, it all seems kind of silly.