It depends what your definition of SF is. If you are talking relative to the incredibly expensive north-eastern part of San Francisco, I agree. But Daly City, etc. aren't that much cheaper than the Sunset/Richmond/Excelsior, especially when you consider that a car will become much more necessary.

That said, SF is more of a place to live if you don't have children (and if you have children, you better be rich). Those with kids tend to live in the suburbs.