It's a little odd. Facebook and Google talk both allowed use of standard xmpp clients when they were using xmpp underneath - so one could get away with a single app to talk to people over xmpp, Facebook chat and gtalk. And eg OTR worked fine.

But both Facebook and Google refused federation, and then phased out xmpp.

I assume all the big players are equally eager to kill email, but haven't quite figured out how yet.