In my opinion one thing that is very different from the US compared to Europe is that labour laws here are pretty favorable to employees. This has the downside (from a start-ups perspective) of having a workforce that is mostly happy.

Happy people are in a strong position to negotiate and will also not easily go and leave their happy well paying jobs in order to be 'repeatedly punched in the face' (that's not mine).

So besides the obvious advantages that an ecosystem like Silicon Valley offers you can bet that if you see a European start-up that the people behind it are extremely well motivated and probably have some funding. As opposed to the 'throw stuff against the wall and see what sticks' strategy employed in Silicon Valley. Typically European start-ups have a higher rate of success than their American counterparts but the magnitude of the individual successes is lower.

This is all from my limited perspective so apply salt liberally.