The actual issue that the full floating axle rule (it is specific to full floating axles), is that on cars with full floating axles, the flange is weak. If you look at a stock car axle, there is very little material where the axle shaft meets the flange. That aftermarket axles are solid in this area. What happens with the car axles is that the flange will break, and that allow the shaft itself to come straight out of the rear end. The hub, wheel, and tire are of course still attached to the car, it's just the shaft that comes out. You would be amazed at the speed that the shafts come out during a launch. I certainly would never have expected it. I have only seen it happen once, and this was on a Chevelle.
None of the truck full floating axles I have seen have this problem, and in fact you are hard pressed to see any difference externally in the factory or most aftermarket axles. Any of the tech inspectors that actually know why the rule exists don't have a problem with our trucks. It's the ones that just know it's a rule, that can cause problems.
The axle retention rule for the c-clip axles is a different rule.
Paul