For example, this question. You can add answers to it, but there is no "add a comment" link on the question or any of its answers. Does this mean we're supposed to "shut up and answer it already?" Or is additional Reputation required to comment?
Commenting on other people's posts requires a reputation of 50, read more about it here. As you have already noticed you can always comment on your own questions.
answered Jun 24 '12 at 17:48
