"Often it's the dropouts that start companies and the PhDs that join them."
I don't agree with your statement. I think we hear more stories of dropouts starting companies because they are rare and make interesting stories.
For instance: 1) http://en.wikipedia.org/wiki/John_Warnock 2) http://en.wikipedia.org/wiki/Irwin_M._Jacobs 3) http://en.wikipedia.org/wiki/Henry_Samueli
. .