See story (here). Oh, part of the problem is that smart people tend to forget that bad things can happen to them. Part of the problem is flat-out hubris. But the biggest problem? If there are no real consequences to bonehead mistakes, then the incentive to avoid those mistakes is very, very low.
Will heads roll at LinkedIn? Maybe. But I don't know if the right heads will roll. Unless the folks at the very top feel the consequences, then the wrong people will learn the lesson about not protecting passwords.