.. it is for this reason that the certification process doesn't consider the potential benefit of NWS.
Can you reference this JT? I have other sources suggesting that it is because the Vmc figures must be correct for both wet and dry cases and NWS would be ineffective in the wet. Alternative explanations are that on some older types the NWS, when used at speed, would break or that the pilot already has both hands occupied at this stage of flight, one on the stick, one on the throttles.
I can't find any authoritative reference.