I think you are halfway right. I think it has to do with vBulletin. I checked some other websites and found there was no tooltip on any of them, except one that had a vBulletin board running.

If you check the second "" smiley from Pureghetto that shouldn't have a title attribute you'll find it actually has. I suppose vBulletin automatically copies the alt attribute to the title attribute to mimic IE's behavior.