Hello, DxO mark lens score takes into account the camera sensor SNR and color sensitivity (CS)
In your example you are comparing those lenses on 2 very different sensors : the Canon 1DS mkIII and the Nikon D4 AFAIK
If you look at those cameras SNR and color sensitivity on the site ( http://www.dxomark.com/index.php/Cameras/Compare-Camera-Sensors/Compare-cameras-side-by-side/%28appareil1%29/767|0/%28brand%29/Nikon/%28appareil2%29/436|0/%28brand2%29/Canon
) you will see that the D4 SNR is 2.5db higher and its CS is 1+ bits higher. This is almost a full stop difference as far as sensor performance is conerned.
This full "noise" stop in favor of the Nikon D4 explains the difference in the final DxO mark lens score which is in fact the information capacity of your imaging system (lens + sensor performance)
You can read more about information capacity here : http://www.dxomark.com/index.php/Publications/DxOMark-Insights/DxOMark-Score