It's reversed. Living in SF is more expensive _because_ the salaries are higher but space is scarce. Salaries are higher because of concentration of high-tech companies which make a lot of money and are not neccessarily pressed to hire cheap. If they were, they'd move these jobs to India anyways.

People come attracted by good jobs, but it turns out it is hard to find a place to live with a good commute. The demand drives prices high.