I disagree with this, simply because grandma wasn't on any AOL chat rooms, but she _is_ on Facebook. The only reason I'm on FB is because Aunt Tilly and Uncle Bob and grandma are also on there, and I can connect with them that way, and know what's happening in their lives in real time, instead of seeing them once a year at Christmas.
Grandma isn't going to sign up for IM or get a blog. She's on Facebook.
That's the difference between FB and everything else that came before it. The thing creates its own gravity field that attracts everyone, and as long as everyone I care about is on Facebook, so will I. Even though I really hate the thing.
That's the genius of FB, I think. Hate it or love it.