If you're right that it's a cultural thing of the investors, what keeps American VC's from going and investing in European startups? (That's an honest question.)
Mostly distance. To manage your portfolio, most of the times you need to do introductions, personal meetings, lunches, etc. That's hard when u have an ocean in between. That being said, each day that goes by there are more US investors setting up shop in EU, which is appreciated :) I wonder though, who runs those shops, Americans or Europeans.