Sorry, I have to call BS on that "it will slow down FT for everyone" line of crap. Completely false.
Besides, who said anything about FT having to host "all" those avatars? Just enable remote images only and problem solved. No storage, no bandwidth, no technical capacity (whatever that is) increase.
Or say they decided to be generous and host "all" those avatars for everyone. If the limit on avatar image size is, say, 30k, that means everyone on FT can have an avatar and it will require a whopping what, 6GB of extra disk space! Hey, I've got a $20 bill right here. Problem solved.
And if the vast majority of FT users don't want avatars then it won't be an issue at all, will it?