It uses the same CoD4 engine, but with a few extra things on top to make it look nicer.
My dad tried to play CoD4 what a 4200X2 and a the top 6800 (forgot what it's called) with 2gb ram. LOL - pretty bad fps. (Ok, he could of got an ok ~25 fps at 800x600 and the lowest settings)
So i admit, they do say
minimum requirements. But they should do, "minimum requirements for a normal resolution and it be enjoyable."