Some moderators seem to have overlooked “obsolete” in this “delete obsolete comments” policy.
In this question, comments on the question contained new information which was not subsequently included in the question. Someone removed the comments nevertheless, and made part of my answer incomprehensible as a result.
I do not mind if moderators remove obsolete comments, but they should remove only obsolete comments.
Gilles, who deleted the comments I referred to, commented on this answer, and explained that it is easy to deduce that my answer on the main site refer to some deleted comment, and therefore the deletion of the comments did not make my answer incomprehensible. That might be true.
However, I still think that he should have incorporated the comments into the question if he would like to delete them. In my opinion, the deleted comments were much more relevant to the source of the confusion of the asker than the body of the question itself. This is why I posted an answer to the question which was not really explicitly asked. (By the way, I also answered to the question on surface, but this is only because I thought that ignoring the question on surface might be impolite.)
If my answer is viewed independently of the question, it might be fine. But Stack Exchange is not just a set of facts; it is a set of pairs of question and answer, where people can post better answers to the questions later. Now that the comments are gone, the question and the answer are no longer related. I do not think that this is how Stack Exchange is supposed to work.