Mark, you may have car axles. Some of the GM car makes used replaceable inner races. Truck axles (at least the AD series) don't have replaceable races, and the bearing rollers run right on the axle itself. Thus the need for machining to use an inner race or weld repair of the axle bearing surface.
Just thinking out loud here, but maybe GM thought the truck axles needed to be larger diameter and not have a smaller diameter where the replaceable seal installs, and a bit more strength by reducing the stress concentration at that point. I think the weld repair that Leon had done would be the best approach to repairing a worn axle.
