I think the issue with marking a thread as "answered" is that this is a forum, not a Q&A site (like Stack Exchange). So there's apt to be a discussion, commentary, jokes, memes, etc. which are discouraged on sites like Stack Exchange. That's not to say you shouldn't follow up on your questions and at least make note of "X works", "Y doesn't work", "Z didn't work for me but might for other people", and so on.
But yes, a lot of Internet dwellers post a question, get an answer, and then disappear into oblivion without ever telling the forum what the answer they used is. You'd almost need a separate website or a sub-forum with a different design to properly have an "answered" question (maybe with votes on answers). It'd be UW.SE, basically.
*nervously checks posts to see if I have any "answered" topics that need wrapping up*