MIT is a lot different than most universitiies. Not everyone can pass or understand differential equations. Just about anyone can pass and understand American History. The latter therefor can be a little more lenient in their admission policy.
That it is. But my point is that they have a very high percentage of Asian-Americans, whereas if they wanted to they could hold it down and still have an exceptional student body. But they choose to favor admitting the best of the best over a quota system.