Who collects friends on Facebook though? I either went to school, Uni, or worked with everyone on my friends list. The only people I haven't met on it are those from VT on there.
I don't class people from WoW as my mates. Sure I talk to them in guild chat, however I wouldn't disclose any personal information with them. Plus I would never consider them friends as such.
I don't think that it is wrong if people do that. However, I never would.
I know loads of people who would class people as friends through facebook even though they had never met. Be it via a mutual friend or jsut common interests, it does happen, and it happens alot.