But you're ignoring the fact that Facebook is effectively the first opportunity in history for a universal "push" mechanism for friendship.
If your best friend died, would you really know how to contact everyone he/she was friends with? You could dig through their Rolodex in the old days, which would cover some percentage but also pick up a lot of outdated contact information and business relationships with no friendship involved; you could send email to everyone you could find in their mailbox, but that surely wouldn't hit everyone; you could dial all phone numbers in their phone, but same problem.
And obituaries are pull-based, and tend to be localized.
FB, for better or worse, has the potential to be the most effective way in the history of mankind to tell everyone who knew someone that person has passed on.