It seems to me that actors in movies spoke a lot better years ago than those today. I suppose in the "Golden Age" of talkies during the big studio system, there was a lot of training including in speech. Then along came the mumble guys and you're so right - the difference between English and American actors is like the difference between people who can sing songs and the ones who can only scream and shout.
Melanie Spyren
read Lia Beachy's article