I think Hugh Laurie, Anna Friel, and Michelle Ryan do an excellent job with their accents. Yes, I have noticed and will admit that Britons rule the acting empire, accents included!
I still can't forget Ben Kingsley's Arab accent in House of Sand and Fog.
I think we should give credit to the linguists that coach them too.
I don't judge a movie, however, by how good the accents are. . I try not to let it annoy me. It's the story these actors are trying to tell that's important.
In my opinion, Willem DeFoe is not that good with accents, but his acting more than makes up for it. Paul Bettany does a great job with accents.
Then again, I don't hear the British accent as often as you do.
Here in America, our speech patterns are so varied among culture, educational and economic status--like many other countries, including yours.
I adore the British accent, I fall into a trance, ahhhhhhhh.
I do not like the way some American's talk--they sound very uneducated, and that worries me, it even embarrasses me as an American. That is why I make my son read a lot of books by British authors, and he loves movies made in your country. Not bad for a 13-year-old!