You're incorrect. The number of M-backspace you appear to need would seem to depend on how many `little' words comprise the part that needs deleting, e.g. foo/2013-03-13 needed three M-backspace to rid me of the date and a further backspace to remove the trailing slash, which isn't insignificant to all commands, e.g. ls -ld bar/ when bar is a symlink.

In comparison. !$:h understands its task at a higher level. And thanks to key rollover, typing different characters, like !$:h, is quicker than tapping away at . until visual feedback, which may lag, tells me I've done enough.