Currently, the filename of the avatar that you have when you make a comment is saved with the comment. If you later change your avatar, the old avatar will stay with the old comment. It would be possible to update the avatar for all your comments, however that would take some extra work on behalf of the database. This way is more efficient database wise. I also like being able to see changes in the site. If you see a comment by someone, but it has an old avator on it, you know that it was an old comment.
I just think that it makes the site look cluttered. It's also easier for me to remember who's who by their avatar, instead of trying to remember by all their avatars. As in, you see a post from someone, you see the avatar, the mind makes an association, and it is followed through in all their posts. Also to combat your "dated message" theory (seeing an old avatar and knowing it's an old post), the date is right there anyway. Just my thoughts behind the query.
I suppose I could allow the option of having all the comments updated when the avatar is changed. It could be something you could set in your preferences. You are free to suggest it on the dev site (dev.caedes.net) if you'd like to insure that I don't forget about it. ;-)
Because an animated gif can have as many frames as you want unless I limit it some way. I don't want everyone to have to download a 30 minute movie encoded as an animated gif.
Thank you very much Caedes! I will set about changing mine! Oh and also thanks very much for choosing my image in the contest! It was a great privilage!