You have asked a very important question. No. They are not similar. Here
is an explanation on how the speed governor for cars works - it used to me mostly mechanical but these days, it is electrical. They work on a basis of limiting
speed by controlling the amount of fuel consumed by the car.
On the other hand, it is different for the CNC. Here, we use a DC signal to start/stop the spindle at the right places, and also vary the speeds. Chris Humpris explains it excellently using his PDF.