No, it is not unusual, but it is a problem.
Some users don't understand the difference between an answer and a comment. The comment text box is the first thing you see after the question, so it's a nice convenient place to simply start typing. Comments even look somewhat like a traditional forum, so it's easy to fall back into those bad habits of interjecting whatever random thoughts come to mind about the topic at hand.
But more often than not, those users simply don't have the time, the complete story, or simply do not have the inclination to post a full answer — so comments offer the path of least resistance. I can understand their desire to offer what little help they can, but the problem is that they're not helping the system by spreading little bits and pieces of the solution wherever they please.
That's a forum problem. We don't do that here.
Comments were designed to simply ask for clarification about the original question. Comments are such a light-weight mechanism, that putting useful information in there can actually be somewhat harmful:
- Comments cannot be properly vetted (voted on for correctness).
- The information in comments is not editable by the community.
- Comments are not easily searchable. When users are looking for your content, they are less likely to come here to find it.
- When users see that a question has been answered in comments, they are less likely to contribute proper answers.
- Questions with comment-based answers remain marked as "unanswered" by the system, so that does not bode well for the community.
When someone asks a question, members of the community are supposed to propose answers. Others vote on those answers so, very quickly, the answers with the most votes rise to
the top. You don’t have to read through a lot of discussion to find the best answer. Answers-as-comments breaks that entire structure.
Discussions in comments are no better than any bulletin board system on the Internet. Every time a new user comes along, they have to read through the initial post, then all the noise in the comments to get the whole story. You end up with valuable bits of the solution scattered among a bunch of noise and conversation. That's a condition we work very hard to prevent on these sites: The Chat Room/Forum Problem.
I understand the urge to interject "just one more interesting piece of advice" when you have something terribly interesting to say. The problem is that other users will emulate what they see on the site and soon a lot of problem-solving goes into the comments.
Every comment that does not belong adds one more broken piece to the site.