Larry, what you've heard makes sense for regular vehicles - add 10% or so
for overloading, etc.

Now think about syncros, and how they can be used/abused off road. Here is a
picture of my fully loaded syncro westie heading down a steep, rocky road.
http://www.vanagon.com/syncros/trips/peters-mill/img/3-wheelin.jpg .

Only three wheels are on the ground, so at max GVW I would have a minimum of
1839 lbs of load on each tire in contact with the ground (5512/3 = 1839).
Also, from the incline shown in the picture, you can be sure that the front
two tires were taking most of the weight...it would not surprise me to find
out that each of the front tires was supporting close to 2000 lbs.

I guess the moral of the story is that calculations help to get a range, but
in the real world the loading can easily exceed the theoretical.

Tom F.