One thing that other commenters may have not mentioned is the illegality of non-compete clauses in employment contracts. You can just ship yourself across the street to the competitor anytime you fell like it. That's not something that VA or TX has. And it's not just tech jobs that benefit from it. All people in CA enjoy that right and often flaunt it.

Aside: One thing that I've often wondered about is how Detroit pulled it all off. MI wasn't the friendliest state in terms of unions or weather back in the day. I've heard that the Miracle Mile was a big generator of Detroit's success as a lab of automotive fail-fast, but I've not thought that as the whole picture. Any good resources?