I don't have stats on this (although I bet somewhere, somebody does!) but I'm pretty sure that if you took all the fanfic stories in which somebody has sex with somebody else, there would be a *lot* more stories about Twoo Wuv than about recreational sex or sex out of sheer boredom. (OK, Torchwood stories probably bias the results somewhat.) Even Hate!sex tends to turn into a revelation of Twoo Wuv.

And, for whatever reason, Fandom at Large identifies penetrative sex as "real" sex and other kinds of sex as foreplay or simply not in the equation.

Also, I don't think there are a lot of fics with kinky sex except in the specific context of a kink meme or a specialized comm.