That's actually kind of obnoxious when you do specify. I mean, I get being disappointed with the umpteenth guy you'd really like a slash line against/girl you'd like a femme line against advertizing for het - I've been there - it's no reason to go off on the poster for asking for what they want.
I actually say this as someone who'd love to find a slash line against quite a few guys I often see looking for het lines. I'm just not going to ask for it in the comments of one who advertized for het, you know? You'd think that would be common sense but for a hobby based around writing, it's really quite amazing how many people seem to take offence at what people write in their ads.