it's not an american trait, it's an internet trait. It's a global community now.
I am an australian living in canada so I am not an american, but I have an opinion which i try to convey, but sometimes get heated if you look at my post history.
If you don't like having someone abuse you then internet forums are certainly not the place. For everything that someone likes there is someone that actively hates it and aren't afraid of sharing that opinion on the internet.
Also Chat Roulette was designed to be a way for people to meet other people around the world face to face using their webcams, but it didn't take long for people to realise that it was also an opportunity to show their penises to the world also.
Just because something is supposed to work one way doesn't mean that is how it winds up being used in practice.
I would think that people in England are just as bad on Forums as they are in the States so you should direct your disgust against the world as a whole. I bet there ar eplenty of Football forums in the UK that are filled with obscenity and abuse, in fact I guarantee it.