The point curiously missing from the C&D article is that a car driving a full throttle will also be generating only a tiny amount of manifold vacuum. In most cars, more vacuum is necessary to provide the power-assist to the brakes, once any stored vacuum is used up. (The brakes will work, but losing power brakes for the average driver will be an upsetting event, especially with a stuck throttle.) They mention "don't turn off the ignition because that will cause you to lose brake assist", but fail to connect the no vacuum at wide open throttle to the same end result.

I'm sure the C&D test drivers were willing to mash the pedal and generate the best braking force the car was capable of. The average person, confronted with a stuck throttle, lost power brakes and the resulting "hard" brake pedal may very well not be able to summon the force required to generate full brake pressure. (It's an amazing amount of force compared to what you're used to using. If you're also the type to worry about flipping the car from putting the car in neutral, you're probably not going to bend the seatback applying enough brake pressure to get the job done.) I think I'd have expected better than the average driver from a trained highway patrol officer, though.

You can't have it both ways. Either drivers are pushing the pedal as hard as they can (which every single driver reports) or they aren't because they're scared.

Either way, your argument is based on a bad assumption. At full throttle in a non-super or turbocharged vehicle, there is still more than enough vacuum to assist in braking.

Another point I didn't mention. The Prius can detect a no-assist situation and will reroute all braking pressure to the front wheels for maximum effectiveness. So even in the extremely unlikely situation you have no regenerative braking and no vacuum assist, you can still stop the car.