This is exactly what Casey Muratori was ranting about in his "Thirty Million Line Problem" video. My interpretation (or extension) of the point he was making:

This is exactly what Casey Muratori was ranting about in his "Thirty Million Line Problem" video. My interpretation (or extension) of the point he was making: if the same hardware (CPU + GPU) can boot Mac OSX or Windows, why can't the same game binary run on both? If hardware vendors created a good "ISA" and stuck to it, it should be possible to write one binary that talks to the hardware directly and runs the same anywhere as long as the hardware ISA is compatible.