This is entirely correct and I know several founders who did so, but thats not really the point I am trying to make (which admittedly I didn't make well)
The question that still stands is why they are moving the the US.
Because the network effect of Silicon Valley is profound.
Investors are looking to fund companies with global reach that will break down communication barriers, render national boundaries meaningless and bring us all close together. . . as long as they are located in California.
Yes and so the question is why does Europe not have anything like that. It does have some places liked London, Berlin and Stockholm but they are all missing a few things.
You're looking at a power law. Just like Cities in a country follow a power distribution of population (I just doubled checked that rule for UK and they indeed follow an almost perfect power distribution) so "Start up" areas will also follow a power distribution - but due to the extreme mobility of start-up founders and capital that will be applied globally not nationally.
Silicon Valley being the pre-eminent location for start-ups is a positive feedback loop which puts it at the extreme tip of the power distribution.
The question that still stands is why they are moving the the US.