And while this author notes Portuguese contacts headed to the UK and Germany, I've noticed the same but with several leaving the UK for the Bay Area (with zero going to the rest of the EU).
This may have a lot to do with getting funding. London has just started to become interested in funding startups, and EIS and the new SEIS are helping, but it is nothing compared to the US. Even the smallest city in the US has more funding opportunities than London. It takes a while for people to change their habits.
That is a (mis)perception most people have (myself included) regarding career development. Professionals follow the path of the higher salary.
For me, the path can be something like this:
South America < PIGS < France/Germany/UK < Rest of The USA < SV/NYC
That being said, there's also people who give more value to quality of life. The place that work for in Spain have several people from The US, Sweden and UK, even though they could be making more money back in their countries.
