Given how the design works, there doesn't seem to be a significant reason to have the entire pipe rotate. It's really the scoops at the bottom that are applying the majority of the workload. They're effectively like the blades of a turbine, with the whole screw acting as a stator.,(reply>), I guess the advantage of the rotating pipe is that you won't have shearing force against the inside wall as the material rises, thus lowering damage to whatever material you're lifting, which wouldn't be the case if the pipe didn't rotate or if you were rotating only the screw.