What do Eric Clapton (the musician) & Hugh Laurie (from the FOX medical drama 'House') have in common?

why or how is it that a lot of famous British people like these two can easily hide their British-root accents for a temporary moment so that they can speak "like an American" in public? it wouldnt be so easy the other way around (since i tried to but with no success), agree? its like when Eric Clapton sings, he does it so beautifully with no detection of British-style english coming from his mouth. but when he puts down the guitar to ready himself for a casual interview, he starts letting the 'expletives' fly! and the same goes for Hugh Laurie (the tall, lanky guy from the medical drama 'House' on FOX). he speaks perfectly good American-english on-screen, but when you hear him talk for real, it sort of disappoints. is it really that much easier for British people (from the UK) to speak like an American than it is for the other way around (like it was for me)? would being 'fluent' in speaking UK english count as a second language?