For example,
Looking for London postcode to area mapping data
It provides a direct answer. Provides a link (the only link) to the data. Was upvoted and commented on by the question asker. How is it different from the other answer not changed?
Why would a moderator change such an answer?
I cannot speak to the current question under discussion (where the answer was converted), but I do have an answer for the revised question (this meta question).
Answers can be flagged with one of four canned responses or a custom 'other'. You can see these by clicking on the flag link at the bottom of an answer. However once that flag hits the review queue, users with sufficient rep can vote to delete the answer with several other canned response options (I can't post an image, because there's nothing in the queue right now and I don't know how to access the options otherwise). Two of those options come to mind as being frequently used: not an answer, should be a comment on another post, or is a link only answer. The mod can choose to handle the flag in a few ways, and I can't tell you what all of them are not being that level yet. But I do know one of the options is converting to a comment to preserve the information that might be helpful but not quite qualify as an answer. I believe a mod can also do this without a flag for the same reasons.
With regard to the answer under discussion, I can see it being considered link-only, but I personally think it was fine. I've seen much worse/more truly link only answers of late getting numerous votes. It may have been related to the Wikileaks source, but that did not seem to be a major point when that subject was asked in another question. In any event, it can only be speculation on anybody's part but the acting mod.
I changed your answer to a comment because it seemed to me that you hadn't answered the question. You gave a link to an old PAF which doesn't provide the neighbourhood names the questioner wanted. As the OP says he can already do postcode to district and ward and that this is not the correct answer he is looking for.
The majority of your answer was a note on the public availability (or otherwise) of UK postcode data which is of little value to the OP or future users.
Something is wrong here. The mod removes my answer and converts it to a comment, down votes my answer, and then answers with their own weaker answer and link. Actually my answer and the mod are almost identical except my link is far superior. On this board ChrisW, Tengshe and myself (as well as the person who asked a question) all think it is a genuine answer. My answer provides the actual postcodes the actual admin boundaries requested and iant only provides an experimental flickr process. This is poor mod behaviour.
