If the dog goes down of its own accord, that's not an alpha roll. That's submissive or appeasive behaviour.
If you don't violently flip the dog, it's not an alpha roll. After all, I frequently roll my dog over when we're playing, but there's a clear difference between that and an alpha roll - one involves violence, the other involves having his feet and tummy tickled.
And finally, I believe that there's a big disclaimer on the Whisperer along the lines of "DON'T ATTEMPT ANY OF THIS SHIT WITHOUT CONSULTING AN EXPERT DOG TRAINERIZER", much like the Dog Borstal and It's Me Or The Dog programmes on this side of the pond.
Final analysis: I'm not sure that what you call an Alpha Roll and what I call an Alpha Roll are at all the same thing.