The closure explanation that appears on duplicates is:
This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.
The last five words of this reason seem rather odd. It is clearly telling the asker to submit a new post, as the embedded link leads to the page to ask a new question. Why would that be the proper thing to do in such a situation? If we are already judging between two questions to see if they are distinct, why would we want to throw a third one in? Now we have to judge between three questions!
I think the obvious thing to do when a question is put on hold as a duplicate but you feel it is not so is to edit the question (or perhaps post a comment) to show why it is not a duplicate. That leaves us dealing with the same two posts, and I believe the system automatically sends on-hold questions that have been edited to the review queue for reopening.
I think that many people understand that this is in fact the desirable way to deal with duplicates. For instance, on this recently closed question Monica added a comment explaining to the questioner that if he thinks his question is in fact different from the other one he should edit to explain the difference and it would be considered for reopening.
Why, then, does the automatic explanation not reflect this. I.e. instead of saying "please ask a new question" it should say "please edit your question to show that it is different". Can this be changed?
Or am I missing something and we actually do prefer the user to ask a totally new question? (The only reason I think that would be preferred is that if the closed question already has answers, editing the question to show the difference might invalidate the answers. But that doesn't seem to justify it, and I imagine there is a way that moderators can see whether a large percentage of closed duplicates already get answers before they are closed.)