[tbirdtbird]

"Seems like the physics of the thing should work so that as the axle nut is tightened the washer pushes against the outboard end of the key to lock it into the hub as the inboard end of the key (with the taper) presses into and upward against the taper of the broached axle slot. "

yes, and don't forget the special 5/8 grease seal, there is a recess machined into the hub to receive it. It somewhat resembles a garden hose rubber washer in size and shape