All languages are going to have dialects. Trying to eliminate that "bias" is going to just result in removing language entirely from exams, unless we decide to make tests for every single test taker. But the point of standardization is to have a solid, uniform goal for all to work towards. And if you're applying to an American university and you have difficulty with what's considered standard American English, you will have far worse troubles in university.

And again, people from families of non-native speakers do well. Generally better than people who only have family who speak the native language and dialect.

That people think it's discrimination is quite clearly silly. :)