To be fair, since we are not party to Apple's strategic discussions, the above may be seen as an effect of Apple's later developments of OS X, but it cannot be assumed to have been one of their primary motivations. It is not unreasonable to suspect that the inevitably doomed impulse to try to include infinite backward compatibility in software is part of what makes Windows the software to know and love. There is a signature of someone amongst the enlisted of this Army that sums up the result of that attempt, quite succinctly. Nor could infinite forward compatibility have been designed into older versions of either platform.
de