I never fully understood why everybody is using XMPP in walled gardens (e.g. Whatsapp, Facebook, Messages...). Do you think they get anything from that? Is any of those services monetized successfully?
At first I did not understood, what it had in special, until I figured that it was the fact that it used your phone contact list, thus taking out the boring task of managing that, and making adding people to your list easy as finding someone phone number.
Yet, I would not use it as my primary messenger (neither Facebook), because of how they are tied to something in particular (phones, Facebook) and thus allow less flexibility in where or how I use them.
I can't even get my friends to click invitation links to pre-baked apps.
Disclaimer: I work at Tango.