Why Don't British Rockstars Have Accents When They Sing?

I haven't been able to figure this one out. My wife and I had a serious heart to heart on the topic, and couldn't find any common ground. How is it that some chap sporting a British accent as thick and disorienting as London fog sounds like Rick Springfield (okay, I don't watch enough Behind The Music...so unbeknownst to me, Rick Springfield is Australian, which makes me an idiot, but actually proves my point if you think about it) performing on a 4th of July float when he breaks into song? How does a rockstar raised in the pubs of Liverpool learn to sing like a perky teen idol raised in Anaheim? Seriously, tell me: when you give an interview to MTV your dialect is somewhere between an orphan from a Charles Dickens novel and a soccer hooligan on a week long gin and quaalude bender...but you pick up a microphone and start crooning like Bing Crosby? You step into the studio and belt out lyrics like an insurance executive in a karaoke bar? I don't get it. What if the Brits won the Revolutionary War? What if The United States wasn't founded in the first place and there was no such thing as an unrefined, bawdy American accent? What if there weren't any Americans? What if we hadn't invented sugary pop music? Would you still sing like us?