> Actually it does apply on unix:

No, it does not apply: here's what I've written:
"""
 rm -f doesn't mean "ignore permissions", but but rather don't ask
confirmation which the rm commands asks in some cases (empty file,
directory, etc).
"""

Having a file non-writable fits in those "some cases" where rm is
extra careful and asks confirmation.: calling shutil.rmtree() on your
example will succeed, so it does not apply on Unix.