This is one of the coolest threads I've ever spent 45 minutes reading (ugh...phew).
Choosing to represent yourself as sexually alluring comes from a desire, usually a subconscious one, to reap the benefits of being attractive. Right and wrong have nothing to do with it, but it's very interesting to think about.
Consider makeover shows, or weight loss shows where a group of trendy experts take typically plain looking people, and give them makeovers or help them lose weight. You'll often hear these people tell the audience that they want their external appearance to reflect how they feel on the inside. It's then interesting to note how everyone seems to feel like a good-looking thin person.
But that has all been said. It's fantasy fulfillment, and it's seizing the opportunity to be more attractive to others, for social or self-esteem benefits. Again, it's not right or wrong.
I also wonder if there's a status difference between people with no signatures, and people with signatures. I just made myself one, and chose to avoid representing my appearance in order to avoid this whole issue. I went with the handcuffs and feather as obvious symbols for why I'm here, and the space image with the quote is a reference to the "LD" part of my name, "Laplace's Demon," which is part of the construction of a particular philosophical concept I found cool when I chose my name a few years ago. Of course, you could probably analyze why I relate myself to that particular concept/quote and glean something of my personality or self perception.
Anyway, I'd suspect that people with no signatures are given less attention. "They haven't bothered to make a signature, how serious and involved can they really be in this community."
Since the creation of my signature two days ago, I've recieved an equal amount of PMs as I had in my previous three-years on the forum. However, that might also be because I went on a posting blitz.
But to go back to the very first post, about that scientific study, I think it's VERY interesting that avatars affect behaviour in real life.