If Google had been started in Pittsburgh, they still would have been successful. I heard about Google through IRC back in the late 90s and immediately switched from Altavista because Google was so damn good.
Incidentally, AlphaLab is new, but Pittsburgh/PA has had seed funding through InnovationWorks and IdeaFoundry for some time. It used to be more like "here's $100,000 and you are on your own." AlphaLab is trying to develop a community. Again, I think it remains to be seen how these seed funding ventures turn out. Admitting SV is the only logical choice is premature. Give it time.