There appears to be a mindset that questions and answers have a 1-1 relationship. That is just not true. In fact it is an n-1 relationship. Any number of questions can have the same answer, and not even be related, or only related tangentially. Sometimes the relationship is obvious only to the answerer, particularly if that answerer is really smart, or highly experienced. Unfortunately, the asker is generally not Sheldon Cooper and they generally have much less specific experience than the hammerer. In my opinion too many questions are marked as a duplicate even when they should not be, or should only marked as a duplicate with an explanation of the relationship between the question and the marked duplicate.
Mehrdad brings up an excellent example. The question was "why do the fonts on my page not behave as expected". All of the answers linked as duplicates are variations on "what is quirks mode, and how does it work?" All of the answers to these questions indicate that Quirks mode is a thing that was come up with to deal with differences in the IE5 markup vs. the standard. And while it may be true that turning on or off Quirks mode may have fixed the problem that Mehrdad was having, "Because quirks mode" only tangentially answers Mehrdad's question, and there is no indication in any of the answers in the linked duplicate questions that would tell a user the mechanics of how quirks mode is responsible for the behavior Mehrdad was experiencing. Thus I would classify any of those answers as low quality answers for the question.
If we want high quality answers, we need to tailor those answers to the question at hand, not just say "because quirks mode" now you go figure out what I mean by that.
Don't get me wrong. I am not advocating writing the same answer everywhere. What I am saying is this is the internet age. Create a new answer, and acknowledge the other great answers to other questions by linking to them in your answer, but don't stop there. Answer the question "how does this apply to me?" in your answer.
For example, instead of hammering that question about font irregularities with a question about quirks mode and leaving it at that, an answer that said something like:
It looks like you are running up against Quirks mode. You can find a discussion about that here, but the reason it can cause the behavior you are seeing is ... and here is what you can do to prevent it ...
Now tangentially questions are linked, the asker has an answer he can understand and use immediately, and the googler who has no idea to ask a question about quirks mode instead of the funky font behavior he is seeing can find help. Everyone wins, and SO is better for it.