I don't think there are less girls, I just think less attention is drawn to the fact. Back when I first joined, there was always a big deal made about girls and we were frequently asked for photos. The environment of the forums was very different, I think the fact there were some girls who demanded constant attention made the rest of us more willing to participate in all of it.
I don't think I post any less, but I generally don't draw attention to my gender. I'll make posts mentioning my boyfriend if it's something that I would mention regardless of who I was talking to, but I don't say "I'm a girl, I'm a girl". These days, I'd rather people assumed I was a guy, because it means I'm just blending in.