When a question has already been answered, we post a comment to that effect. It may be automatically generated via a duplicate question flag or vote, or it may just be a suggestion in a comment. The comment will read, "Possible duplicate of [link]", or something like, "This may already be answered here [link]", or "See if this answers your question [link]".
We don't want duplication within SU, so there is a specific objective for doing this. However, the result is that we use a comment to provide a link and say, "look over there for your answer."
If the answer already exists outside of SU, there is not the issue of duplication. However, exactly the same information is conveyed in a link-only answer. Almost everyone agrees that link-only answers are not desirable, but we're doing some complicated debating over whether they are acceptable, at least in some cases.
In another question (Move link-only answer to a comment?), there was a lot of qualifying in the answers.
- Link-only answers are low quality answers (not comments).
- If it's accepted and upvoted it's considered helpful.
- Moving these to a comment is one possible solution, at least in specific circumstances.
However, the "default" categorization of link-only answers is that they are answers. They can be moved to a comment, at least in some circumstances. However, having been posted as an answer instead of a comment, the objective is heroic measures to improve it rather than simply re-categorizing it.
So "Look over there for your answer [link]" is a comment if the link is within SU and an answer if the link is external. Other than the link's location, there is no substantive difference in the post.
If a link-only answer can be an answer, why can't a duplicate question notice be an answer?
- Is it only because of where the link points?
- Is there some question vs. answer distinction? The duplicate question notice refers to another question, but it is valid only if the answer is there. If the question isn't flagged, the link often points directly to the relevant answer.
- Is the basis because the author chose to post it as an answer instead of a comment?
I'm not suggesting that they should be answers. I'm trying to understand why they are treated so differently when the content of the post is the same.