I'm often find that the comment box doesn't do all of the things that I want it to do (like newlines for example).
In this question, for example, I found myself posting debug instructions, that just wouldn't format very well had I posted them as a comment.
Now, these debug instructions are not the answer, nor are they part of the answer, but they're for information gathering.
Content-wise they probably are better suited to be a comment, but had I posted it in a comment, it would be hard to read and might be more likely to be ignored.
I think it might be useful if you could post richer content in comments, especially newlines.
That way, you can write those kind of comments so that they can be more readable.