I doubt the league actually has a greater number of American born white players than in recent years. I think there are some more white players on higher profile teams, which changes perception. Also, the emergence of Kevin Love as an All-Star, and Dirk Nowitzki winning a championship this past summer, have kind of raised the profile of white players in general.
I would venture to guess that there's a greater number of mixed-ethnicity players in the NBA than in the past, however. Guys like Blake Griffin, Stephen Curry, and Kris Humphries are representative of the NBA's future, I think.