Personally, I think we need to distinguish between unanswered questions and unsolved questions. Questions with answers are not unanswered, but could be unsolved if the answers are poor.
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I agree there is a semantic difference, and there is a corresponding display difference (0 answers and red box vs N answers and green box). However, from a use case perspective, I believe grouping them together under the same tag is preferable. If the user wants to personally be more selective, the visual indicators are there to allow for that.