Maybe not in general but among interactive fiction and visual novels (the only thing I browse around here) there's a lot of them. There's over 5k erotic games, about half of those are visual novels. I don't have any concrete numbers but among my searches, it feels like 1 out of every 5-8 games is some kind of porn. I will turn on / off the setting but I'm not happy with having to do this every time I want to include or exclude adult content. This is something that should be part of the search / filter engine.