While some may insist that once you delete your Facebook account, messages you've sent and are in others' inboxes, groups you have created, tagging on photos (actually do they, at least does the UI indicate who tagged?) should be deleted, I think it is actually reasonable to expect:

When I delete my account, any files (photos) I have uploaded are deleted. I don't care if I tagged someone in another photo which I didn't upload, it's their name there, not mine. If a message I sent is in someone's inbox, I obviously don't have any control (actually it depends, but let's take it this way).

It's like if I deleted my email account, I expect my inbox to be deleted, not an email I sent, which is in someone elses inbox.

It's not just that though. At all large organizations handling data, it is processed into several databases, statistics, aggregations, archives. There aren't any systems that can keep track of all this and purge all the data correctly.