I answered that very question in my post above.Hi schlitzaugen.
If the rear and front axles were rigid and not sprung, would you still pursue your argument?
If you had the vehicle front and rear axles as rigid (unspring) and sitting on individual scales, the load figures calculated by Fordman still hold and would be reflected on the scales.
You are confusing that the rear (and front) axle is a pivot point and suspension concurrently. It reacts in response to changes in load.
I agree weight on the axles would change even with a rigid chassis, but you have to be careful again in calculating how.
My suspicion is that the position of the centre of mass of the entire vehicle dictates where the fulcrum point is. Which is why I think you are afflicted by the very confusion you project on me.