Even if they do prefer the city now. I just can't come up with a scenario where it makes sense for people to crowd in cities over the medium term. Heck, I can't make sense of why companies like Yahoo and Google insist on co-location, especially by tech companies, in this networked world, especially in vastly overpriced places like SF or anywhere in California for that matter.
I have a theory that co-location, especially in tech has more to do with tax and accounting policy and incentives than anything else.