Hardly anyone is Bill Gates. He and a few others (Zuckerberg) have led people to romanticize the notion that dropping out of school is the path to wealth.
The most recent Forbes 400 list of the wealthiest Americans I found (dated Sept. 2010) has only four people in the top 20 who do not have college degrees. Among those four, two are involved in Microsoft (Gates and another) and one (Christy Walton) inherited her wealth through marriage.
Meanwhile, Warren Buffett (#2) has an extensive education including a MS in economics. A large number of the top 20, in fact, have multiple degrees. The Kochs (in the top 5) both have multiple degrees from MIT.