Source: Microsoft [TechNet]
quote: Most PC games will barely use two cores, most of it leans on the GPU. Crysis 3, a very new game, is the first that really benefits from quad core. Others like Bioshock Infinite and Tomb Raider don't.
quote: I can list some off the top of my head that use more than 2 cores.
quote: A game is processor-intensive with a load that cannot efficiently be spread around since a lot of the calculations are intertwined with each other and cannot be split apart, processed independently and returned as they are completed. Even if the load is split, it still needs to be recombined and it still needs to wait on the main thread. This adds processing overhead, increases memory usage and adds a thick layer of complexity to the code among other things.