When we first started taking avatar requests the original file size was always 50 x 50. (I should know since I was the one that worked on them all heh) It's not something new, it's just that people starting bending the rules as time went on.
There is a reason we have file size limits, it's not like we're trying to be a-holes about it.
The original 50 x 50 was to keep the forums from losing their look (didnt want to b0rk the left table) and a file size limit is in place to keep people from uploading 3 meg avatars.
Anyway, doesn't matter now as someone has changed that to 60 x 60 again.