The part numbers are different for the motors between the KEB and REB, but that doesn't mean that the motor internals are necessarily any different (all models of TSC-55 REB share the same motor). It could be the shaft and arbor on the motor is modified between the two models to allow it to hold the different width blade or fit in the machine slightly differently, maybe different windings to control the blade brake, along with a modified housing to prevent cross-fitting the motors between the saws. The electronics package is also different, which makes sense to incorporate the anti-kickback.