[Kevan]

OK, let's go back before Esc's were invented, I raced rc cars in that era too. 
Cars had a wiper resistor operate by a servo, the exact same wiper resistor seen in parma controllers. This was the speed control and could be operated by hand with the transmitter off if required.
In a slot car setup that resistor is in your hand control not in the car, the car is connected in series via the track. 
When Esc's started coming out in the 80s, my first was a Demon I think and that was electronic rather than resistor, later becoming mosfet and mosfet 2.
So it's not the same thing at all, the variable resistor is still in your hand controller whether it's a brushed or brushless setup.