Probably this is a duplicate of 221 unanswered questions but now there are 1408 unanswered questions! This mean that the problem far from being solved, is getting worse.
A frequent type of very old unanswered question is an occasional users that make a confuse question and never reply to comments asking for clarification. In this case close as "not a real question" has been proposed since this mean a 'free' downvote from community that accelerate the elimination of lower quality zero answer questions. I think that is a good solution, but in practice is not working well, whereas another policies as closing duplicates are very effective (a clear duplicate often remain open only a few minutes). May be this policy must appear more clearly in the help pages or somewhere?
But more many other old questions are legitimate questions that has been already solved long time ago with a comment. Close as "off-topic", "not a real question" or "too localized" seem inappropiate in these case, but after months or years of no activity, their unanswered status is only useful to hiding the questions that still need an answer.
What is correct way to handle this questions to remove from the "unanswered" group? Answer "This question has been solved in the comments" although the answer will never be accepted or up voted? Put a flag? Down vote? Vote to close for the above concepts? Nothing of this seem appropriate in this case. What about a new feature: Vote to change a comment in answer and/or mark the question as solved in the title?