Okay, hockey night beers have worn off, time for serious, non-sarcastic posting.
Yes, Ork is indeed the new Black. In addition to the reasons you listed, 'trog' has roughly the same connotations as the n-word. The setting sometimes even treats them as direct analogues to blacks, what with orksploitation and that Ork and Mindy program from No Future that is clearly equivalent to Guess Who's Coming To Dinner. But most of what you said can also be said about Hispanics in America too and the setting doesn't shy away from having ork-Hispanic comparisons either, so 'trog' is also 'spic'. Orks and trolls are also into rock and roll and the heavy metal scene, as evidenced by all the setting fluff about 'trog rock', so they're pretty white too. In some respects, it's as if orks and trolls are poor people rather being an ethnic group.
Then look at elves and dwarves. At first glance, elves seem like white people plus, and the setting does treat them like that sometimes (again I point to Ork and Mindy). But they're a minority, if one of the better off ones, and they think they're better than everyone else. They're also seen as exotic and desirable, they stick together in the face of a majority and build their own part of town....elements of east Asians, perhaps? And dwarves might also seem like white people plus, but again they're a well-off minority. Well, they have a secret society, and in Chrome Flesh Haze made a remark about dwarves always having money.....my knee-jerk reaction is to say that Dwarf is the new Jew, but since nothing suggests they have heavy involvement in banks and the media it's nowhere near a perfect fit. Again, this might be about money rather than race, since elves and dwarves are both better-off minorities.
And all that is just looking at it from an American perspective. Go elsewhere and the stereotypes about metatypes are different. Go to Britain and you'll probably find that orks and trolls are into lad culture, which is as white as mountaintop snow, yet are also Pakis. Go to Scandinavia and you'll find that Trogs are the new Finns, getting drunk all the time and being mean, violent drunks by their nature. Go anywhere that is dominated by one race, and you'll find that race can be broken down into smaller ethnic groups, at least one of which is economically disadvantaged and has unpleasant stereotypes which are projected onto the local orks and trolls.
In short, orks and trolls are thought of as violent dumb brutes prone to criminal lifestyles and being poor that people are generally afraid of while elves and dwarves are the genetically and socio-economically privileged; whatever groups, be they ethnic or socio-economic, you'll see them as stand-ins for is reflective of the stereotypes of your cultural upbringing.