Huh, interesting. Personally I don't like this -- or at least I don't like the idea of hardcoding Gravatar support.
What I would prefer would be the ability to choose an avatar provider (granted, Gravatar is the only one right now) or accept OpenIDs and look for either hcard, SREG or some other link type (rel-avatar?) to enable decentralized avatar serving.
As well, if you want to enable remote sign ins, for example, using Facebook Connect, you're going to want to enable generic discovery or serving of remote avatars.