This seems crucial to me - most of these 'nondiscoverable' actions are shortcuts, and there is another discoverable way to achieve the same outcome. They are similar to keyboard shortcuts in that way, they just help power users who know them.
(The calculator backspace seems to be an exception, which is why I also dislike it.)
There isn't a backspace in the calculator, but the swipe is still (basically) a shortcut for something which does have a button. Pressing the C button clears the current input entirely, after all.
(The calculator backspace seems to be an exception, which is why I also dislike it.)