No doubt, historically the UK has produced a lot better popular musicians than the US.
The Beatles
Rolling Stones
Pink Floyd
Led Zeppelin
Sabbath
but the US can hold it's own
Beach Boys
Bob Dylan
Bruce Springsteen
as for currently, there is very little that is popular on either side of the pond; when talentless hacks like The Darkness (who are just copying things done 20 years ago) can become popular...it's a sad state of affairs.
As for the Sex Pistols, they are criminally overrated constantly. They were a mediocre (at best) punk band; UK punk had become somewhat of an accepted institution in the UK (much the same way, say, gangsta rap would be now--younger people don't really care, but the parents are deadset against it). After the punk thing faded away in the UK, THEN the US' best punk music came; Anti Flag, X, The Germs, the whole LA scene, the DC scene (I recognize that bands such as MC5, The Stooges, and The Ramones predated or were peers with most British Punk, but I am making a generalized statement that the 80s punk--aka hardcore--was the US' best and most important contribution to punk music).
Overall rock and roll, i'd have to give the edge to the UK; Led Zeppelin and Black Sabbath started (for better or worse) heavy metal. The whole blues-rock thing was mostly made in the UK (Zeppelin, Cream, etc), which is surprising, as blues was a more popular music form in the United States at the time.
Pop-rock (which the Beatles dominated) was again to the UK. Despite the best efforts of bands such as the BEach Boys (Pet Sounds is undoubtedly on par with Sgt Peppers, Revolver--any Beatles album), the Beatles just had MORE great songs than anyone else.
OK, I'm tired of typing and am going to breakfast