Yep - in fact it would make more sense to me if SO not only allowed duplicate questions, but also added a decay such that even highly-rated Q/A pairs would even

Yep - in fact it would make more sense to me if SO not only allowed duplicate questions, but also added a decay such that even highly-rated Q/A pairs would eventually get overtaken by newer content. Questions and answers just aren't evergreen things that one can expect to last through the ages. And even if they were, treating them as such means that SO's new users generally can't contribute anything. I find SO's current model really bizarre.