My Facebook account is so barren that it has never existed, but if I'm ever forced to create an account to deal with websites that assume everyone has a FB acct and can't deal with you otherwise, it will be as sterile as I can make it.
And my Twitter account is so sterile that no one I know follows me. And yet, it's a real account.
The thing is, do you have only 5-10 FB Friends with eerily similar sterile accounts in a little-self contained social graph? Have you added a college to your profile, but have no Friends from that college?
I've got a fake FB account for the same reason you describe, and I don't bother go to the efffort of puttiing in the sorts of fake details that these accounts have.
And my Twitter account is so sterile that no one I know follows me. And yet, it's a real account.