Yes, this is a cultural difference. I follow the website fmylife.com and I've been astonished by the number of people who complain about their "purity rings" (not having kept the promise) or that their parents caught them having sex or losing one's virginity to someone who had a bet he'd manage to sleep with the girl.
So, first of all, Americans try to protect their children from sex. They want them to remain "pure" until they get married (and even after that, if possible).
Secondly, because the topic is taboo, it turns into something nasty to be discussed with friends groups. "The walk of shame" as a term illustrates the idea - it's cool to get a chick drunk, do her, then in the morning she feels ashamed and you tell all your friends and you make fun of her. I never understood why I would make fun of a girl who slept with me. I never saw this as degrading - it's a matter of honor. And I am left with the impression that in the US this would be a source of ridicule.
However, Europe is not homogeneous from this point of view (and I suppose the US is not, either). Our neighbors, the Romanians, are similar to the Americans from this point of view. The parents of my 21-year-old ex-girlfriend thought she was a virgin and it was a serious issue when she told her mother she was not. On the other hand, they do it like rabbits within their friend-groups and do not break-up until they find a better partner. So, for them it's enough to be with the best available option. And this is sooo strange for me as I am always looking for "the one" and it's totally natural to just break-up as soon as I make sure that there is not too much future in a relationship. :)