Paul Graham’s Y Combinator leaves Boston, entrepreneurs dive under the bed
muckandbrass.com
muckandbrass.com
but afair hn/yc was started solely by pg with jessica's book release shortly thereafter, at least that was the impression I got. other guys must have joined later (or they kept low profile before)
He acknowledges that his startup was 100% bootstrapped and profitable. In those happy circumstances it doesn't really matter where you are located, unless taking venture capital would help you grow faster (if fast growth is your goal).
However most startups wouldn't exist without some capital, and Silicon Valley has the highest concentration of wealthy tech investors. Those investors like to be able to keep a close eye on their investment, ergo all the entrepreneurs cluster where the money is.
Anyway, the point he's trying to make is that it doesn't matter much where your start-up is based in today's day and age.
From a semi-outsider perspective, the entrepreneurial community in Boston seems fairly healthy even without YC.