$40 per user is roughly inline with the $3B Facebook was prepared to pay for Snapchat (though we don't have precise numbers on Snapchat MAUs).

This is another defensive move. Hundreds of millions of people sharing rich media in realtime on non-FB services is a genuine threat.

It's really a direct result of smart mobile devices. Facebook used to own the user's contacts, but now independent apps have direct access to device contacts without Facebook.