To serve as a warning to others.
It's not polite to mock the stupid. But when a major company like Apple does something quite this astoundingly dumb, the only real option is to propagate it as a warning to others. And I don't mean just other .mac users. I mean other tech support teams or webmasters who might think that sending out passwords to unvalidated addresses is a good thing.
(Or root SSH keys, for that matter. You know who you are).