From: William Corcoran
I think it's a bit more interesting to uncover
why rm does not remove
directories by default thereby obviating the need for rmdir
On early PDP-11 Unixes, 'rm' is an ordinary program, and 'rmdir' is
setuid-root, since it has to do special magic (writing into directory files,
etc). Given that, it made sense to have 'rm' run with the least amount of
privilege needed to do its job.
Noel