Marmoset is a game engine? You mean like engine like Unreal3 or Source kind of engine? If so why haven't I heard of a game created with it [or was End of Days one, that one game that got the horrible rating?] So you're saying I can use Marmoset with Maya? That's a revelation to me.
not knowing about the way their engine works, but for "large scale" shadowing the multiplication is easier/ more efficient to do. While a more correct lighting would look cooler in a modelviewer, it wouldnt be truth to the ingame engine anymore, which was the point of the app