Sure, but a lot of forums allow crazyass filesize - mostly because the admins are too dumb to use the admcp

However the bandwidth has nothing to do with my descition to block animated avatars.
It is in my opinion, as earlier stated, screenspam which steales focus much more than a static 64x64 IMG (unless you do a goatse or something). My users love this rule, and there is never any complaints.