I'm not much of a businessperson, but I wonder why startups cluster in expensive places like South Park. You could move to a loft in the East Bay, not too far f

I'm not much of a businessperson, but I wonder why startups cluster in expensive places like South Park. You could move to a loft in the East Bay, not too far from BART, and save enough to pay a whole other salary, maybe two. pg's thesis about Silicon Valley is that it's mostly the about the investors. I assume that the talent pool is willing to do a BART ride to the East Bay for the right startup. So is being smack dab in the middle of the cluster that vital to success? How does the math work out?