I agree that there is a contradiction in the moderation: on the one hand, you get moderated if you update a question/answer ("because it has to reflect the situation of the author when it happened"), and on the other hand you get moderated when you ask a similar question ("duplicated").

I find it okay to not update the answers: just like a blog post or a newspaper article, I find value in being able to say "this person had this problem in 2012, and this other person provided a fix also in 2012". But then it should be fine to ask the exact same question a couple years later if one expects a different answer. And it should not be marked as a duplicate. If anything, it could be marked as a duplicate after the answer is accepted, if it turns out to be the same (and if the new question has no value). But in reality, when I am stuck on a problem, I don't mind checking 5 similar answers. It's much better to have to find a solution from 5 similar questions than to not find it at all because it was moderated away.

Also it would keep people engaged: the current policy means that for some topics, it's very hard to contribute questions/answers because there are so many already. But in reality, many of the existing ones are more than 5 years old! If people could repost similar questions and get points for answering them (instead of being flagged as "duplicate"), it would probably keep the community more engaged.