Crysis IS multithreaded, but yeah, it doesn't put four cores to 100% each...To do so, you have to use 2d games like Prime 95

Crysis just uses what it needs and that is not bad coding, once the limitations present in the game come from current GPUs lack power, and not CPU power.

As for multi gpu scaling, we all know the current AFR techniques suck very hard, so you can't complain the engine on that...