I do agree that if you are building a revenue focused company, you don't have to go to San Francisco.
But it's hard to argue against how easy it is to raise money or get acquired in the valley vs anywhere else in the world. Look at how easy it was for Path and Instagram to raise money and to get cheap money at that. In other markets many VCs want to see revenue not just traction and that revenue can work against you and lower your valuation - making the money more expensive.
For reference to Instagram, see this Chris Dixon interview with Kevin Systrom
"He also talks about how the serendipity of Silicon Valley contributed to the formation Instagram, remembering a party that Dixon once threw in San Francisco where Systrom ended up meeting his key angel investors."
http://techcrunch.com/2011/02/02/founder-stories-instagram-l...