To expand further on what Oli said in the comments, I would argue that duplicates should only be used when both:
- Any answer to question "A" would also be a valid answer to question "B"; AND
- Any answer to question "B" would also be a valid answer to question "A".
If either of the above two conditions aren't met it's not a duplicate question.
In the case of a more specific question being nominated for merging with a more general question like in Braiam's example, that should not be considered a duplicate because answers to the more specific question would not all be valid answers to the more general question. The same would be true in either directionregardless of which one would be merged into the other one - that is, if the more general question is merged into the more specific question it still remains a problem.
You can certainly still refer to a more general question as part of an answer or comment on the other question.
Remember it's questions that you're merging, not answers.
The questions can be worded differently or have different details that would not affect the answers given, and still be duplicates if any conceivable answer to one would also answer the other.
Naturally, very specific questions are rarely going to be suitable candidates for merging because their specific details will be relatively unique in ways that would affect how people answer it. This is a good thing; we don't want to bleed the diversity out of questions by removing what makes them specific. There is a place for specific questions here just as there is a place for general questions. In theory people will be searching for content based on specific keywords related to their problem, so if there's a question that's a more specific match to their problem it should in theory come up highly ranked.