Its to promote brand recognition, brand power, and to brand their directory, site, or search engine. They usually go for half whateever your signature goes for. When someone "buys" your avatar, signature, location, or anything, they are technically renting it for one month, unless they state they want it for life.
I'm still waiting for someone to buy my location and blog feed . its good money , might as well make some money out of the forum while I'm here .
http://forums.digitalpoint.com/showthread.php?t=501288 Guys, you might wanna give me some competition unless you want 2,437 posts to end up having a wacko head transplant for an avatar for a month!!!!
If they can handle 12k of your avatar around here, they should be able to handle 2k of a wacko head transplant!
There are things worth more than money. Your avatar is your brand and more valuable than a couple of dollars.
It is good for brand identity. Also, people do visit the URLs mentioned in the avatars, so it is also useful for traffic and to improve business.
for money ofcourse. if your avatar is attractive enough, people will would like to see what's the site about. I'm one of them who will go to some site from avatar if i like their design and have a catchy slogan.