It really could be because the 480 Ruger can be loaded with bullets seated out, with the only limitation being the length of the cylinder over all. If that is available, there is no loading difference between 480 Ruger and the 475 Linebaugh.
It is just like a 44 magnum bullet with a crimping groove set to maximize the available space in a Ruger Redhawk revolver cylinder. It effectively is putting the weight outside the case and that allows more powder to be available inside the case. Just my opinion though.