Okay, bearing in mind that I've been awake since 4 a.m. for work, I think I've figured this out. Having a hot chick avatar is sort of like playing as a female in, say, Morrowind. I think I heard an explanation once that it's sort of like having eye-candy to look at while trekking across the same boring trade-route for the millionth time. So, if he gets bored while reading the forum, he can just twitch his eyes to the left and be less bored.
Of course, the logical way of doing this without offending sensitive people would be to not maximise the browser window, have a hot chick as the left-most bit of one's desktop wallpaper, and yeah.