This video is readily available on YouTube. In my own experience the QuietRock -- on its own, as replacement drywall -- stopped neighbor conversation at normal volumes and muted TV at normal volumes.
Even with the best drywall, a loud stereo with lots of bass might produce soft thumps, and direct impact against a neighboring wall (hammering, door slamming, etc.) might still come through. But the noise is significantly reduced. One thing to consider in some instances: if you only soundproof the wall, but not your ceiling or your floor, some noise might come through in those untreated areas.
I agree that most construction -- at least in the USA -- is done cheaply without insulation and by using ordinary gypsum nailed right on the studs. I'm amazed when I see construction sites and see ordinary drywall getting unloaded!