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Well, os.waitpid() on Windows also takes a process handle. 
This was (of course) deliberate, so that os.waitpid() could
use the thingie returned by os.spawn() on Windows.  If
os.kill() were ever added to Windows, I think it would be
quite natural for it to take a process handle too, and for
the same reason (Python code mixing os.{spawn,waitpid,kill}
could be the same across platforms).  Zope's ZODB relies on
mixing spawn and waitpid this way, and Zope's ZRS implements
its own kill function on Windows so that the rest of the
Python code can just do kill(id) on all platforms (where
`id` is always something obtained from os.spawn()).