mm

Hmmm, " All writers remove every word on!"

mm

Oh, wait: " All writers every word!" etc., etc., etc.

mm

No ESP on the A4/S4 so far in the US. Only Audi knows the reason, and they are not talking.

Flying Billy

Pretty good description. However you have included one misconception. When an open differential has one wheel spinning, say on ice, no power or torque is delivered to either wheel as the torque is always equal on both axles.
Rate of Power = torque x speed(rpm) x a constant. If the wheel spins freely there is no torque, thus no power is transmitted. ***Motion is not necessarily power!***
When you are stuck in a rwd car on ice you can sit with the wheel spinning at idle and even get out and push. The engine will not stall as long as the wheel spins freely as no power or torque is delivered. Only motion.
In terms of work (power), work = force x distance. If force = zero there is no work. That's why you are stuck.