Royal "drop-in" motors are, indeed, self-contained units. When you purchase a drop in motor, it includes the commutator, stator, both bearings, cooling fan, carbon brush assemblies, and more all in one package. For a "drop-in" motor replacement, the old motor simply emerges from the rear housing (the housing that looks like a space alien helmet) whole and the new one slides in its place. Essentially re-attach the wires and the suction fan, and you're good to go!
Non-drop in motors are not like this. I've never taken apart one of this type, so I don't know the exact procedure, but it is my understanding that components such as the rear bearing, brush holders, and stator are each independently fastened to the rear housing.
You can tell these motor types apart by looking at the rear housing. "Drop-in" type Royals have no externally accessible carbon brushes and no oiling ports. In contrast, non "drop-in" motors do have these features. The "drop-in" motors have sealed, maintenance-free ball bearings supporting both ends of the armature, whereas the other kind of motor has a sealed, maintenance-free ball bearing supporting the fan side and a sintered sleeve bearing at the other. The sleeve bearing requires occasional oiling with a non-detergent oil and thus has an oiling port with a red cap.
If I recall correctly, some of the oldest Royal motors may even have sleeve bearings supporting both ends and therefore have two oiling ports: one at the rear and one under the handle bail.