Every place has a specialty so I wouldn't say everything happens in SV. They just happen to be more web focused than a lot of other places. Want to do finance computing? NYC. Government and aerospace? DC-Maryland-Virginia metro. Movies and VFX? LA.

Obviously there are outliers, which have a rich cross section of talent, Miami, Chicago, Charlotte. But if you want to get a web-based business up and running and need a deep pool of talent there is no better place than Silicon Valley.