Obviously there is a selection effect that confounds any causal comparisons between those who do and do not get into MIT. But the better counterfactual is students who are accepted but do not attend. A diff-in-diff study with these two groups would be a better test. There are unique features of MIT: more money, elite network, etc. I do share your skepticism though - I've worked w/ MIT people before. I think they are very smart but also very lucky.