That was just my school, 5 years out of graduation. That might change in another 5 years as bankers get to MD levels, and then have a client and relationship roster that they bring to the buy-side. There are also people who switched to Tier 3 or Tier 4 buyside firms, but then don't make the kind of money you make at a top PE or HF.

Also, I did not go to Harvard, which typically sends more people to the buy-side then the other top-tier programs (but is somewhat self-selection, because HBS tends to accept a lot of pre-MBA buy-side people from top firms)