The weight of the Rover was probably an equally big factor. The D might have had better chances with locking hubs front and rear, but I'd put my money up against Tom's (willing to lose it too) that the Rover could still beat him in that case, just because the Rover weighs so friggin much.
Nevermind, I'm thinking of the full size Rover, and the GVWR on the D is actually heavier. Disregard my stupidity and carry on.