well, as much as i like to spit on fb privacy fuss... the truth is that you could actually delete your account for a long time now.
few months ago i did right that. ok, there wasn't a button, but if someone searched for something like, ummm, 'how to delete an account', he would get a link that would do just that among other answers.
and regarding the ability to remove slashdot account... someone wrote that user doesn't gain anything from removing slashdot account :)... while this might be true, it's simply silly... i don't want my nickname to hang around... maybe i have ppl that know me by my nickname... it might be a thousand things. if one can create it, he/she should be able to destroy it.
let's be honest, in that aspect is fb one step ahead.