Besides, having the ability to attach a comment to the URL does't mandate putting anything in it. It's suggestive to the submitter that they should make the effort though else their submission might not compare well against those that do.
And if a submitter thinks "Oh, this article isn't really good enough to spend my time on summarising" then that's a good test of whether they should inflict it on the rest of us in the first place.
Rant over. :-)