There isn't a panel of experts answering wiki questions. There is instead a wonderful group of people, who enjoy helping others. Individuals, other members, will answer questions in a field they know something about.
As far as comments - if the comment is specific to an answer it makes more sense to use a comment directed at the answer.
I frequently comment on original questions, if I have something to say, but want to make sure that other people read the question also, because sometimes if a question is already answered, I for one won't actually bother to read it.
I guess an answer, answers the question, and a comment is not necessarily an answer, but frequently clarifies or adds to what has been said before.