4WheelUnderground
Suspension is EVERYTHING
It's been a rule of thumb for longer than that, but it still does not explain why the rule started.
The OEM's use it. They use smaller tires and I've never seen them use anything thicker then 1/8" wall for the brackets. Would make perfect sense that all their studdies from decades past tell them its the budgetary and surefire way of taking care of the engineering as quickly as possible.
Thats a total guess, but it makes sense.