This question already has an answer here:
I often get the comment on my answers that "this should be a comment." They are right, it should be, but I can't because I need 50 rep to comment on questions.
I think it should be possible to comment without rep because many people out there are asking themselves questions to clarify other questions. For example...
User a asks: How can I set a dyndns on my router?
User b responds: Have you looked at the firewall settings on your router?
It's not really an answer, but it's good enough that it could lead him to find an answer himself. It's pedagogically better because now he knows the solution, and got the "I did it myself" feeling.
My problem now is that I can't help them help themselves the correct way, because I can only answer, not comment!