The question is can you afford to purchase any property in Manhattan, even with the salary most may get? There are quite a few companies in Toronto (startups as well) paying over $120K for well versed engineers. I can't say it's the norm but it's not impossible to find.
But having lived in SF myself, I can tell you it all balances out if you're thinking of settling down in an area. The cost of housing, healthcare (if you're part of a startup that doesn't have full insurance coverage - only my partner who worked at one of those big companies you dislike was offered full coverage comparable to what you'd get in Canada, well slightly better really), etc all add up while that's adjusted for up here.
Depends on how you measure it?
You're right and I don't expect everyone to flock here. It makes sense for certain people, but I always like throwing out stats like these: http://www.theglobeandmail.com/report-on-business/economy/ec... as BS as they may be.
In the US my "backup" plan is working with more talented, well-funded people on some other thing. In Canada my "backup" plan involves drop ceilings and fluorescent lighting.
I would have agreed with you 2 years ago but more and more I see amazing companies take off here. And again I've lived in SF as well so I know very well what you're talking about and it's the main reason I suggest a lot of new grads to hang out down there for a few years before coming back up. It is a huge reason to still live down the states but there are a ton of cool well funded companies here as well.
Also when there's 300,000 Canadians living in San Francisco, most of that talent you're talking about is Canadian anyways!