My co-founder Adrian asked the AirBnB founders that question believe it or not! They said they always planned on staying in SF and that's where the heart of the company was. New York was just where it took off first and they thought that if they could nail the model there, they could do it anywhere. Turns out they were right.
It felt far away from it when I was there, but I believe it could become more ingrained with time though. I think it's very clear that there are great investors (USV is world class) and companies/founders at various stages (eg. Kickstarter, RapGenius) in New York, but there's still a bunch of missing pieces in the ecosystem that SV has nailed down.