I think the question is not why tits get hits, but why tits get hits but not many comments. The ratio of comments to hits is notably low for pinup type pics - why is that? Are they really typing one-handed? Are they just too embarrassed to comment in public? Are the kind of people who click on boobies not the kind of people who comment on art? It's a reasonable question, I think, especially if at other sites, erotic images do get comments.