(Personal opinion) It isn't the United States that's attractive. It's the tech-hubs within it. I would never seriously consider moving anywhere but a handful of cities / areas in the US. The eco-systems in those places are still years ahead of London or Berlin.

I moved from Sweden to the United Kingdom to attend university for similar reasons. The university culture is different (much better) here, and there is more of a hub factor to the campuses, which offers many advantages socially and otherwise.