You might be right. I am talking from personal experience. When I got off the boat some 22 years ago I discovered that US social life is rather dull comparing to what knew from Europe. Most of my subsequent travels are consistent with that observation.
As to the frequency of sexual encounters - I just reported what I read in an acclaimed study, but I expressed my skepticism. I think surveys are notorious for misrepresenting non-public behavior. But having said that, I think that the image of "oversexed US" is a myth - in reality the US is probably not much different from most other countries. What is different is that US-ers like to talk about sex in public, as well as use sexed-up images as a marketing tool - which tends to be less frequent elsewhere.
Wojtek