They are much easier to mold like clay. White males aren't used in media so often because of inherent sexism and racism in society, but because they are the least restricted by culture and belief. White men don't have a culture, they've scoured the world for a long time and done it all, unlike a lot of other races which seem to still adhere to specific religions and cultural beliefs. So if you want to make a fantasy game, it's a lot easier to model the main character as a white male, someone who can be seen as anything, instead of as a man or woman who comes from a very traditional area of India. White men don't have origins anymore. They are easy to imagine in any role. They're much easier to picture in combat roles because that's typically how history went down, women were not mainly front line fighters.

In a lot of ways, society has contributed to the destruction of the role of white males and their culture, so it's partly their fault the white male is now the standard model for everything. You've destroyed his identify while allowing other races to preserve their culture, he's easy to put in any situation compared to others now. This makes a lot more sense to me than devious sexists ruling every media outlet. On top of all of this, white men have very easy to understand voices for most of the world, and male english speaking voice actors(http://en.wikipedia.org/wiki/Steven_Blum) are typically the most well known and talented right now besides Japanese VAs.