Why can't some questions be commented on?

Question

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?

Answer 1

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.