Bahaha!!! That's just good family comedy right there. (side note: that was a joke.)
Additionally, many things come into play here. For one, there's a huge gap in ratio of men to women here on this sight to begin with, so, regardless of the preference of the female, you are going to get more posts from men because, well, simply put, there ARE more men. 
Also, many of the women here are interested in tickling/being tickled by men. So they wouldn't be inclined to comment on the picture of another woman, regardless of the body part.
As to the f/f ladies here or the men posing as such, I can't even speculate because I don't fit into that category at all. 
So being one of the ones interested in tickling/being tickled by men here, I'll comment as to why I don't comment on such photos. Simply put, I don't know your "wife/girlfriend/significant other". And for me it's about a connection with people, even if it's just a base familiarity with them. To me, commenting on such pictures is the same as making the same comment to a stranger. Just not something I make it a habit of doing.