I think there are two main issues that stops Europe from becoming a start-up hub, too:
1) a cohesive market, which is also your first point. EU is huge, bigger than US, but the market isn't very cohesive at all. The first time I heard about the EU Commission wanting to push for turning EU into a "federation of states", much like US, I was pretty pissed off, because I know that just means increased corruption at the top, with fewer people having more power over a huge region.
And I still think that's going to happen, unfortunately. But now I also think we can't turn down the advantage of having a cohesive market like US. Maybe if we can delay it into 2020's, by then the Internet will make things a lot more democratic, and it wouldn't be so easy to be corrupt at the top of EU.
2) I'm not so sure it's genetics. I think it's the culture, but not even the "entrepreneurial American culture", but the Silicon Valley culture.
First off, there's no "start-up center" in Europe, certainly not one as concentrated with entrepreneurs and especially investors, as Silicon Valley.
And second, people aren't used to "pitch their ideas" to investors, which are few and hard to find to begin with. There may be a lot of rich people, but they aren't actively seeking entrepreneurs to invest in their ideas.
So it very rarely happens. That's why you don't see start-ups that "change the world" from Europe, because while a start-up getting millions of dollars just based off an idea is kind of a daily occurrence in Silicon Valley, it almost never happens in Europe.