That's not quite true. From personal experience at two different Ivy Leagues schools, I can say that these schools and probably top schools in general are completely obsessive about fulfilling certain stated or unstated "requirements" for students. Yale, for example, where I went for undergrad, prides itself in having students from all 50 states--I can pretty confidently say that, if you're from a state with a smaller population, or simply a smaller number of people who are interested in attending a school far away, your chances of admission are substantially higher (think Montana versus New York).

As others have pointed out, although admissions is need-blind (it is not relevant whether you're rich or poor), I'm sure that socio-economic factors are also evident from where the student went to school, recommendation letters, information about parents and their professions/education (which are often asked on applications), and so on. So, while race may be the most obvious "discrimination" point, this is really, in my experience, not the case. And given these multifactored assessments, it is enormously difficult to "prove" that schools are discriminating based on race: it is NOT the case that the school gives everyone a number, and then increases or decreases that number based on your race, wealth, etc.: compare Gratz v. Bollinger (http://en.wikipedia.org/wiki/Gratz_v._Bollinger) (point allocation system where underrepresented minorities received more "points" on their application illegal) with Grutter v. Bolilnger (http://en.wikipedia.org/wiki/Grutter_v._Bollinger) (less-rigid race-based affirmative action permissible).