I think it's probably to do with how people are marketed. I'm sure there's some push from their agencies etc to change their last names etc.
A lot of 'white' actors have done this as well, Tom Cruise, Natalie Portman, Charlie Sheen all changed their more ethnic names to more convential ones. Did you know Natalie Portman was Jewish? I sure as hell didn't
There have been lots of articles about how Asians (from China, etc) have been getting plastic surgery to look more Hapa (mixed ethnicity). It doesn't suprise me really though, look at all the famous Asian actresses, even in Asian magazines they look mixed.