Mike Gotta makes an interesting observation:
Communication vendors have held rank for the most part and have focused almost exclusively on SIP and SIMPLE. XMPP and Jingle have been viewed as "radioactive" by some vendors. Same goes for Microsoft.
I like it! Yes, XMPP is dangerous if you're trying to control what kind of apps developers can deploy. But if you want to encourage creative mashups and innovation at the edges, then the deeply hackable real-time XML streaming technology we've been building out for the last 8 years is just the thing you've been looking for.
The choice is yours.