at least US is not like Japan... (yet)
In Japan the media that is available to the younger female audience does not portray them in actual sexual acts but rather on them being the target of sexual desire. US TV puts them as being not the target of it but rather direct participants (initiators).
Of course the media for older audiences does put young females in the role of participant but this media is not available on the airwaves (its like a premium cable channel you need to pay for) and when it appears on magazines its sold with the same caution as Hustler is sold on any store in the US.
Your handle and avatar comes from Strike Witches which is a perfect example. It has fanservice and the main characters are underage girls... the show is heavy on sexual-based humor like breast size envy and such.. but you dont see them behaving like sluts or actively going at each other in bed which is practically what live-actor media in the US portrays underage characters lately.
sex sells indeed... and where in Japan there is immense social pressure against improper sexual behavior there is practically none in the US.