http://telepathy.freedesktop.org/spec/Protocol_Interface_Avatars.html is a draft. It should not be! This needs implementing, presumably in Gabble.
Yeah, I need it in Empathy as well https://bugzilla.gnome.org/show_bug.cgi?id=615257
Fixed in git for 0.21.5
*** This bug has been marked as a duplicate of bug 20775 ***