One thing about having larger available sizes for avatars is the amount of variability between each member's avatar. If it was changed, some would want to keep their 60x60 or smaller image while others would have them ranging from 60-100x60-100. I'd think it would make the forums look less uniform.
Another thing is this: for the members using the EoFF 2.0 skin, increasing the height limit of avatars would create more empty space between the postbit information and the actual post content. Still a uniformity thing.
If it weren't for those two things, I'd agree with you.
