User blog comment:DaNASCAT/Technical Update: May 24, 2011/@comment-3104099-20110526064557/@comment-1656630-20110526164011

Yep, we got that added in for comment editing, thanks to Anne Behnert's suggestion. But now that i look at it, it does seem a little strange that we didn't add one for comment-posting, too. Though the use cases are different... we don't need to cancel out of a new comment nearly as often as we need to cancel out of an edit.