Even though I'm a guy, I like to use female characters on the internet as a "metaphor" for what I am in the non-physical sense.
In third-person-view games, it's partly a practical decision; if I am going to spend hours staring at the character's backside, it might as well be a girl's.
But if it's a display picture, then it's much more of a symbol to others of what I am. Depending on what I feel like at the time, I'll draw an approximation of my physical self or an approximation of my mental self. And my mental self seems to like being represented by a female character, so that's how I draw it. (Her? What? )
Oh my gosh I totally understand. (Especially about staring at the character's backside for hours! lol!) And online I usually do opt for a male character or ambiguous name. I was setting up my Steam account with my boyfriend and he immediately began typing my name as "Kumagoraa" and I had to stop him. I had top sit and seriously think about if I really wanted such an obviously female name (even though it's a nonsense word and doesn't actually mean anything.) Least to say, he gave me a strange look XD (Though he's used to it by now though...)