Cryo engine treatments have been around for more than 12 years now. And when you do the freeze, it will do just what the article says. Armed with that you can understand how cylinder walls, pistons and valves won't stretch (as much, if at all) anymore, tolerances remain tight and like Asmall said - capable of running really lean conditions or even some alternative fuels (Like water injection on a gas engine... it can happen if the seals are good)
Rotary guys like cryo treating - The size of the motor allows it to be cheaper to actually perform, and at the same time the apex (Not seals, but the apex) doesn't stretch so far in high RPMs.
-> Steve