I really mean that no other big chat service federated back. The global network of federated XMPP servers was dwarfed by Google's userbase. Maybe if AIM/MSN/Yahoo added an XMPP bridge they would have kept it.
I seem to recall there was a brief period of time when gchat federated with both XMPP and AIM, and I was using Gajim to chat with users from both of those services without a bridge (or at least, the bridge run by Google/AOL was invisible to me).
Was Facebook messenger ever _federated_ though, like GChat was? You could use an XMPP client with messenger, but you couldn't talk to people on other XMPP servers like you could with Google Talk, from my recollection.