My guess is that this is a direct response to Microsoft.
Google has been talking open-ness, and xmpp is part of that. Microsoft decided to connect messenger so that they could send messages to g-chat users, but didn't reciprocate in terms of allowing g-chat users to see messenger contacts. (I don't know the protocol, but I understand this is a valid use of an xmpp server, even if clearly parasitic).
Google have responded by shutting the whole thing down. 'Hey Microsoft -play nice, or we'll take our ball home'