What the Bay Area does have is a greater concentration of talented engineers than any other major municipality. When you're trying to make a concrete decision where to locate your startup, that matters. And most of the people who argue "Don't move to SF" aren't actually arguing "Move somewhere else", it's usually "Adopt a distributed team where you pick the best engineers regardless of location." The latter approach has a bunch of its own problems, so it becomes a tradeoff of getting the biggest possible talent pool possible vs. reducing communication costs and building a team locally.
[1] http://en.wikipedia.org/wiki/Joy%27s_Law_%28management%29
Just joking, but I think your logic might be slightly missing some other important factors.
(FWIW, I personally have little interest in supermodels...but then, most people would consider that lack of interest = "not willing", so the logic still holds. Like all logic, it obscures subtleties - I'd be quite willing if she were a good match beyond being a supermodel and I weren't already attached - but then, this is a problem generally with imposing words on the world, and not with the specific instance.)
Keep in mind, I said "willing to go," not that they were already there.
The numbers indicate that many more are willing than those who are not.