I also used to think that, and in the long-term I agree, and I have (i) done a startup in Europe (failed for lacking of funding) (ii) worked for a European startup (Prezi). But right now I work for Facebook (in London), and this is a good thing. You can go to these places and learn a lot, a lot more than what you can figure out on your own with your friends sitting in a garage or at one of the moderately successful European startups (moderately successful=0.1% of Facebook, that's already like $300-500M), which any sane entrepreneur here would be super happy over, fully so.

By "a lot" I mean cultural things, vision, strategy, how to set your own expectations, how decisions are made, what tools are available, etc.