I don't even have a Facebook page but I get friends of friends email requests all the time asking me to join their Facebook page. I also know a few authors and empowerment coaches who invite people to join their pages to get tips and the latest info, and share a community experience, or whatnot. They have lots of "fans" on their wall (or whatever it is called.)
To me, Fb seems to be a lot about just becoming popular, significant, "famous" on FB and collecting a lot of Friends or in the case of the authors I know, Fans.

I would think there are people trolling around in these more public pages, hoping to gather info from the unsuspecting, saying "Hey, I'm a fan of Loren's too.

(Loren has got over 3000 fans on her wall.)
Also, what about all those games like Mafia Wars? I heard you actually need to get on teams to try to win the game. So, people may be likely to accept people to their page.
There was a recent thread here where the OP's DH found out he may be the father of a teen, with a woman he slept with years ago. She INFORMED him on his FB page.

Another person here kept getting FB updates on her ex when he was creating lovey-dovey posts to his current GF. that's just TWO examples where people let all kinds of people access their pages.