an explanation for vanishing friends

I'm using the new Facebook layout on my personal FB profile just like everyone else is. I was perusing through the menus and whatnot, checked the friends list portion and saw this:

Nobody was pixeled-out, that was my doing to protect those people's privacy. What I noticed was the generic avatars. The names were next to them, but what was with the plain avatars since nobody uses those?

I click on one and find out:

Ah, okay.. I think this is a new thing. Or if it's an old thing, this is the first time I've seen it. Even if someone deactivates their FB account, they still remain on your friend list just in case they ever reactivate their profile.

More people these days are dumping their FB profiles due to, shall we say, a disenchanting experience with that site. My only reason for using FB is for the fan page feature, because I almost never post on my personal profile anymore. If it weren't for that feature, I probably wouldn't have a Facebook account at all.