While I agree with all the procedures which you describe for dealing with this...

I really really doubt what you have attributed the reasons to ... "the axle shafts are the motion limiting devices " ... this would violate a whole bunch of principles... and they could not be made strong enough to do that....
I suggest that the shocks or a strap or something else is the final limiting device for wheel drop....I am sure someone knows for sure on this and will post soon.... I know that on the wagons the shock is listed as the travel limiting device...