It does seem to be a cultural thing in America, as far as I can gather, and they probably think we're really weird for not doing it routinely. Is it a hygiene thing over there, as some have said? Whatever, I think it's a fairly major thing to do when the child isn't able to choose themselves to have it done.
I remember the programme on TV about the English boy whose circumcision went a bit wrong (they cut too much off!) so they brought him up as a girl, thinking at the time with the nature/nurture debate that he'd never notice and would be happily a girl. Which he wasn't. It was a fascinating programme but scary to see how much doctors and parents will risk.