here's my logic:
people choose things they like as avatars, usually reflecting what they think of theirselves or what they imagine themselves as.
It may not actually look like the person, but that image gets ingrained in your mind as a connection to that person, so whenever you see that or a similar picture, you think of the person. Like insom with einstein or forty-two with marvin the robot, or malak.
That's the reason i picked phoenix wright as my avatar. He's professional, yet a bit rough around the edges, but in the end he always gets the job done.
it's more intelligent than you may think =P