Any email provider also has your social graph. The only problem with email is that it is seen as "old" compared to the "new" of Facebook and Twitter. Something else will come along and be the new "new" and that will be the end of Facebook.
They really don't. Not the way Facebook does; not for the post-Millennials. People email bosses and professors and acquaintances; they use Facebook for friends.
Any email provider also has your social graph. The only problem with email is that it is seen as "old" compared to the "new" of Facebook and Twitter. Something else will come along and be the new "new" and that will be the end of Facebook.