If the answer to a proposed duplicate question can be solved by the accepted answer to an existing question, but the new question specifically asks about a specific tool/technique then is it really a duplicate question? Or just a duplicate answer?
There are many ways of solving problems within unix platforms that may not be applicable to a one or other *nix variety, or the asker may have specific restrictions with regard to the command they want to use - even it is just for educational purposes. Eg. a question could be asked about grep that has solutions in sed, awk, perl, etc.
Commenting and pointing the asker at other techniques to solve their problem, including other questions with answers, is all very good and helpful, but is it fair to call it out as a duplicate question?