I think it's reasonable to keep content for 30 days, like holding it in a trash in case you want to restore it.

Other than that delete after 30 days thing, I was under the impression that deleting your account removed content permanently.

I seem to recall servers crashing here, there, and everywhere in the 0.18 (or maybe it was 0.17) days when a user with a lot of content deleted their account (which I presume was fixed).