One last point, everyone seems to be forgetting the incidents and accidents that have occurred when the engine has failed to respond on a PFLWOP that has been initiated by closing the throttle.
As you rightly say, there have been numerous events of the type you describe. While it is usually difficult to say for certain the reason the engine has failed to respond on practice forced landings, especially if there was no obvious mechanical failure, investigations have usually pointed out the weather conditions were conducive to carb icing; exacerbated by the pilot forgetting to use or incorrectly using, carb heat during prolonged glide at idle power. That is an entirely different subject to the discussion points on this thread