<p>Comments are not answers.</p>
<p>The purpose behind embodying a comment in an answer is to bring some finality to a thread: it thereby receives a definite reply on which users can vote.  The question will no longer be considered unanswered by the SE system, either.</p>
<p>The principal danger to relying on comments to answer a question is that the comments could be wrong!  Thus, reposting those comments carries some weight.  It indicates someone has thought enough of the comments to believe they are correct, that they adequately answer the question, and they are willing to risk a bit of their reputation on that.</p>
<p>Generally, we consider answering older questions -- regardless of the source of the answer -- to be beneficial to our site.  We encourage it (and so does the system, by potentially awarding various badges for answering questions that have received no replies for a month or more).  Flagging late answers would be helpful only when those answers violate site norms so badly that they should immediately be edited or deleted.  (Examples include spam posted as answers.)</p>
