The better analogy to those would be if someone had said social networks in general were going to die off.

The land-line has been effectively killed off (the last X million accounts will be slow to go, much like the last X million AOL accounts have been). Facebook would be the land-line approach, social networking voice telephony in general.

Vastly more people now get their email through a web browser - "webmail" - than via dedicated desktop email software (eg Outlook). Facebook is Outlook, social networks are email in general.

I'm not saying Facebook will die like that of course, rather your comparison is all wrong.