I think it's fair to say that there are good and bad tourists/expats from any country. Unfortunately it's the bad ones you always notice. Being an expat rather than a tourist is, of course, another story but in some defense of the ones who are unhappy... there are quite a few who frequent this board and other boards who came here only for love. And doing that is a completely different kettle of fish than deliberately planning a move to another country for some other reason (work, school, adventure). It's not necessarily an excuse, but I think it's safe to say that the rose tinted glasses of love can blind you to all the other hurdles involved in an international move.
I'm actually the opposite of the typical loud American student... I'm really shy and quiet in class. But I've seen other American study abroad students only here for a semester who act that way, and I'm pretty embarassed!
I'm pretty quiet in a class environment until I get to know people better. That said, when at Reading Uni, I sat in on loads of undergrad lectures and was utterly dismayed by the complete lack of response by the British students. They were too quiet as far as I was concerend. Totally different to anything I'd ever experienced at in many, many places in the US. It's one of the reasons I worry about teaching here rather than back in the US. Encouraging class participation seem like pulling teeth. This was brought home to the UK teachers at my Dept when a group of American undergrad students came to visit. The Dept staff delivered many of the same lectures the deliver to their Uk students and the response and feedback from the Americans blew them away.
But hey, that's just my personal experience!