Well, actors are acting!
And, interestingly, Hugh Laurie is just about the worst example - and perfect example - of Brits "singing American".
Hugh got great praise, from Americans, for his authentic sounding American accent in the "House" Tv series BUT when he sings the blues, rather than singing in his own voice, he adopts this dreadful American voice.
Now, this is the perfect example of a singer "acting" at singing the blues.
Now, had he adopted a character - called himself "Professor House", or something - and made it clear that he was acting out the role of a old-time blues singer, that would have been acceptable.
But as it is, he is the worst example of a charicature performance and I want to laugh out loud everytime I hear him.
But, my view will carry the day! There will come a time when Brits "singing American" will be viewed as silly, in bad taste, and just plain embarassing.