Tell that to the people who write L.append(1, 2, 3) despite that it was never documented. :-(
I do -- if and when I see that (haven't seen it in ages). Technical managers at development shops know about stuff "accidentally working" and are more tolerant of bug-fixes against that than of other backwards-compatibility breaks, in my experience.
Hm. This was widely complained about, probably because many examples (including in books) got it wrong. Maybe technical manager are tolerant of that stuff, but not if it means they have to fix their won code. :-(
--Guido van Rossum (home page: http://www.python.org/~guido/)