How about the brain chemistry of asian compulsive gamblers? You can be in the middle of Ohio where it's 99% white people, step into a casino and it's chinatown.
That probably has to do with cultural preferences for the type of gambling that's happening in the casino. I'd suspect pretty strongly that if you looked at other forms of gambling (lottery tickets, scratchers, bingo halls, etc.) you'd see a more representative cross-section of the population.