The official reason for Google to give up on this is that there was a real problem of incoming spam from lousy domains, and no major player wanted to play the federation game with them. It's not as simple as you make it sound.
1) they are able (forced to) handle spam for Gmail (and internally for gtalk) - I'm not convinced by the spam argument.
2) there were only two "big" players, Google and Facebook. The benefit of federation would be as with email: an open internet with federation across organisation level services (community/company run servers).
The fact that Google didn't implement ssl for federation doesn't mean people "wouldn't" federate with them, it mean Google didn't make a real effort.
