In Chicago, where I'm located, this is our core problem too. It's all about that first round of winners. I think startup scenes really launch after the employees from the first big win sell _their_ companies.
But now, FB or Google employees are like, wow, that was awesome, let's do it again. I think the startup scene is more mature now and that reinvestment is more likely to happen outside of SV now -- the key difference is that startups are more stable, wiser, far leaner, and more `cool' now, so it's seen as an actually "safe" bet to re-invest. I know if I ever had a win that's exactly what I would do, in fact being able to re-invest is a lot of my motivation for being a founder.