I doubt Automattic runs Gravatar for free out of the goodness of their hearts. It can track in two easy ways: firstly the user that requests different avatars,

I doubt Automattic runs Gravatar for free out of the goodness of their hearts. It can track in two easy ways: firstly the user that requests different avatars, as they move through the web and different sites, and secondly the users whose avatars are requested, as to what services they use. Their privacy policy allows for this at a quick glance. Personally I proxy Gravatar requests through my web service's backend to get rid of the first type of tracking.