MIT and Harvard are brand names. And because of their name they attract bright people. Quality in quality out. But, I have seen some very dumb people out of HBS. Last time I checked Harvard's application (over 10 years ago) I saw that they stress more on family background and ties (if you are son/daughter of a CEO, or Senator, or a Governer, you have bright chances) then individual persons background and capability. HBS has sons and daughters of Presidents/Prime Ministers/political heads from several countries.

But degrees do help.