I understand the value of physical proximity to lots of other like minded, smart people. However, I would have thought that the tech crowd would be the first to decry the inefficiencies of having one or two (SF and NY) annointed "tech hubs" and actively eschewing every other place. Why crowd every damn programmer in the world into the SF bay area when we have the internet?! That's the whole point of the internet!
There's also the cultural argument. Tech work has tended to attract people who are part of non-mainstream culture. Tech hub cities attract these people because they already have every culture and subculture imaginable and a society that mostly tolerates them. There's also a perception that other places don't have this and that their particular affiliation would invite outright hostility. That's mostly not true. Every large city (>1M people) will almost certainly have communities of people who share your culture or at least tolerate and support it.
Again though, I think that choosing where you live based on whether or not you can surround yourself with exclusively like minded people is counter to the hacker ethos. Let's not forget that Silicon Valley was not always what it is now. People built the place, and the rest of the US and the world could benefit from people who attempted to do the same elsewhere.