The wheels just ride independently on bearings, they aren't connected by an axle like in a RWD vehicle.
I think you misunderstand the true purpose of a differential. A ring and pinion is necessary to take the rotation of the driveshaft and change it's rotational axis. That is, the driveshaft is spinning about an axis from front to back of the vehicle and something needs to convert this rotational force perpendicularly to turn wheels.
True that differentials (non-spools) allow one wheel to "slip" but that is a design to handle that scenario rather than the true intent of the differential.
I hope this makes sense.