When editing a post, pressing Esc does the same thing as clicking the "cancel" link: it cancels the edit. However, when editing a comment, pressing Esc does nothing.
Could pressing Esc when editing a comment cancel that edit as well?
A keyboard shortcut to cancel a comment does not make sense.
When you edit a post, canceling will ask for confirmation before you lose any changes. If you didn't make any changes, this convenient shortcut will quickly bring you back to the original screen.
But comments are created inline. If you didn't enter any text, there's nothing to jump back to. But if you did enter a comment, one slip of the finger will send your text to the great *poof* in the sky. So we would have to add an "are you sure" confirmation. That doesn't make it much of a shortcut. Where's the upside?