Thanks for mentioning this. I was getting real confused about why someone would create a CPU/ASM for their game. Thought he'd then have to build the new game on top of that CPU and notch is crazy but that seemed a bit much..
It's not completely unheard of. State machines are pretty popular in FPS's, and the Infocom Z-machine code is still used (although upgraded quite a bit) for modern "interactive fiction"/text adventure games.