Lots of companies pay head hunters good money to get valuable candidates. You can think of the Ivies and the other top tier schools as 4-year head-hunting agencies. They first do a selection to see which kids have the most potential. Some of the kids have potential in the fact that they are very hard working, or extremely smart, or both. And some have potential in the fact they have a strong personal network (the legacies). On top of this selection, these universities also provide training. But that's secondary.
