I think the dogfooding nature of meta probably makes it unique from a “deletion policy” perspective. Many communities will use other tools like issue trackers, wikis, etc., which all have their own artifact version control built in. Because Discourse is about facilitating discussions, generally a deletion policy has its place for users of the software. Open source projects might delete some conversations, but wouldn’t delete bug tracker tickets simply because they’re outdated, and wiki pages should generally get updated/revised rather than deleted.
So that said, if those types of data that would otherwise be in a wiki or issue tracker are retained vs. deleted, then my point that @mcwumbly quotes above becomes moot.
* Now I’m not saying that this actually happens, and there are more than enough wikis that have outdated pages for various reasons, but this is just used as an example.