It all comes down to a basic understanding of elementary physics. To maintain equilibrium, every action must have an opposite and equal reaction. This goes for forces as well, and we assume that the gravitational loading remains static (if the gravitational loading is changing it would be nearly impossible to evaluate!). All the WD system does is re-arrange how the gravitational loading is reacted to by the ground.
With just that basic understanding, I don't don't believe it would be appropriate to interpret "distributes tongue weight" to mean "changes gravitational loading", which is essentially what the opposing argument in this thread is worried about.
I'm going camping - have a great weekend!
