Having moved to the Bay Area from Boston when I started doing startups, I can say that the problem is more of a structural issue than just "not letting the next big one get away."

Whenever we talked to East Coast VCs, they wanted our startup (pre-revenue and basically pre-product) to have a clearly defined business model and revenue strategy. In doing that, they do somewhat reduce the downside, but they also eliminate the very top of the bell curve.

West Coast VCs seem to have much more of a shoot for the moon mentality. While the latter does lead to a lot of flops, it seems like it also yields some huge winners that the more conservative approach may miss.