Terry, I don't know that much about the history of the config files.  I do know that during framework installs of Python on OS X, the "install_IDLE" recipe in Mac/Makefile.in (which ./configure uses to produce a configured Mac/Makefile) has some editing steps, using sed, to alter the IDLE .def files as they are being installed.  I'm attaching the two edited .def files as installed by the OS X installer.  And then there's the runtime munging of "Alt-" to "Option-" in GetCurrentKeySet() of idlelib/config.py.