Hrm. Interesting question.
Thing about yaoi is it's largely by girls for girls, and this shows in the material. It's usually quite sweet.
Whereas the heterosexual mainstream hentai stuff would be a bit more harsh.
Usually involving innocent little girls being violated somehow.
I think that's why sometimes I'm drawn to yaoi. In most cases there seems to be an aspect of care in the relationship.
Wow. Was I just open about relationships?
The internet is a scary place!
Of course there are exceptions. We have some uber sweet guys here (Hi Roku

), and some very dirty minded girls (Mrawhow), but I think generally the more female orientated stuff makes me feel warm when I'm feeling outwardly cold, and yeah, the more hardcore stuff is only of use when I'm in a dirty mood.
It's all about moods. o.o