Cory,
I appreciate what you say and have argued for years against the use of spring washers in proper joints.
However it is a fact of life that many assemblies are designed and built to a price, often in the face of fierce competition. I am not talking about motor cars, but toasters, washing machines, computers, furniture.
Everything in life is a compromise; strength, weight, cost etc., and sometimes the market won't pay for anything better. I think there can be a valid case for specifying a shakeproof washer.
Jeff