Matt Yglesias is right that the Valley isn't quite as meritocratic as Tim Lee thinks it is, but he missed the obvious point in both his examples. Bill Gates and Mark Zuckerberg are both dropouts from UMass-Cambridge. What's more, Gates' father, Bill Gates Jr., was a very prominent lawyer in the Seattle area before Microsoft ever did very much. Both men almost certainly relied on social connections granted to them by their membership in the intellectual/academic elite to get their businesses of the ground. Indeed, the response to Michael Arrington's troll-bait piece on race in startups points out just how serious the problems of faux meritocracy can be in technology.
One could argue that the tech sector is more meritocratic than finance, politics, or journalism, but that's an extremely low bar.