Hm. It took me a minute to think, because it's not really a sex act that registers with me (it's neither a kink or squick), but Harry Potter fandom does have more of that kind of thing than the previous fandoms I've been in (X-Files, Joss fandoms, Farscape). I think it has a lot to do with, yes, the fandom being so full of incredibly transgressive sex acts and plotlines that you hardly notice something like that amongst the incestuous bloodplay chan.

I also think, though, that the fan demographic makes a difference in that HP fandom tends to associate really kinky sex acts with heightened romance, and I think that's because it's a younger generation of fans. It's hard to imagine cumshots featuring prominently in, say, XF fandom, where the fans were predominately middle-aged and there was a lot of domestic slash. HP seems to run more along the lines of "bondage + dirty talk + making Character A watch Character B blowing Character C = OMG A/B forever!!!" Which is cool, just an adjustment for me. *g*