nodrama,
The step is probably not designed as a stop, it is far too narrow. If you look, there also is a similar step undercut at the inboard end of the bearing seating. This is probably designed so that the inner races very slightly overhang the seating at each end and so, there is no chance of the inner race being wedged up on a radius at the inner end and at the outer end the spacer can also fit against the whole outer end face of the inner race. These bearing races are very hard but quite brittle. Any unequal or point loading can cause fracture.
OAP
This is basically correct. But the "grooves" are stress relieving grooves ground or cut on a radius to prevent a sharp right angle on the shaft material. The outer edge of the inner race of the bearing also has a radius for a similar reason, in addition to ensuring that the pre-load clamping covers the flat face of the bearing without putting any radial force to it which could lead to misalignment.