Based on what? Let's not pretend Microsoft suddenly decided to deactivate a perfectly working machine, they deactivated a machine that in their eyes had undergone a significant hardware change.

I'm (seriously) very interested in learning how California law can invalidate an EULA that applies to the rest of the world. If Microsoft were randomly turning off machines for the fun of it then I'd be in line to sue them, but the user is on record explaining what he did to make it deactivate itself.