Viewfinder magnification is a fairly important specification, although it's not discussed too often. The bigger the viewfinder the more you can see, and the more you can see the easier it is to compose and frame a shot. Viewfinder coverage is something Snapsort seems to have left out of their equation. If coverage is less than 100%, you can end up getting things in your final image that you didn't see in the viewfinder.
Yes, the 1D X and 1DsIII have very large viewfinders. That adds I little to the cost, because the pentaprism must be larger to support the larger viewfinder. Viewfinder magnification is one area where the 1D X is clearly better than the Nikon D4.