Heh, I don't think it's about the relative whiteness of the player (says the whitest guy ever), bit of a dangerous generalization there really. IMO, saying it's more about how much exposure to different lifestyles and/or viewpoints they've had as a result of their education, upbringing, and choices in life might be a better plan. And while that CAN be tied to ethnic background, you really have to stretch it to do so.
In my opinion, it's more about intent, theres a big difference between players who play to play, players who play to be someONE else, and players who play to be someTHING else. It all comes down to what you're looking to get out of the game. Most folks simply don't want to be something completely different, they want to be themselves, only better. The alliance races provide that. Horde requires thinking more 'outside the box/body/what-have-you".
FWIW: I play to be someTHING else. Hence, tauren. Plus, it appeals to certain parts of my ancestry...
p.s. folks who play forsaken as "just crazy humans"? TOTALLY missing the point. But again, just one guy's opinion.