This is all good knowledge to have, to be sure, but I think we're
wandering afield from my original issue - I didn't want to ask about the
default OpenGL coordinate systems, I'm reporting that the same code
behaves differently on a Mac in a window than anywhere else.
Run the code fullscreen on a Mac, it behaves as I expect. Run the code on
a MSWindows PC, it behaves as I expect.
I'm proceeding with the understanding that this is a known and resolved
bug in the Mac SDL code and will be fixed when the 1.8 (final) binaries of
PyGame are ready.