They aren't the same things at all.
Technology inevitably moves on. What was posted as a valid answer 8 years ago is very likely not valid now. I'm sure most people recognise that. Look at StackOverflow - by far the most comprehensive website of tech Q&A, yet it's absolutely littered with out of date material. Nobody cleans that up, you just accept that a lot of answers aren't valid, and move on. Besides, you never know when there's a grain of truth/value in old threads, which may give someone a steer on how to solve their problem. I don't see that leaving these threads around does any harm, and would take a considerable amount of time to clean up. There's no system resource impact, other than taking up a bit of database storage. Easily solved by adding more storage, or periodically purging/archiving the database schema, which I'm guessing does happen at some point.
