TV ads should display the effectiveness of the product whenever possible - it helps sales. For instance, in a car commercial the car zooms around, showing of its style, control and speed. In a Swifter ad, we see the Just-Above-Average-Looking housewife cleaning (an already spotless) kitchen floor. Infomercials do nothing but show you the product in action. Relentlessly.
Rosetta Stone doesn't do that. They show people using the software but we never hear them speak this new language. We don't doubt the validity of their celebrity endorsements - you can watch Olympic Fish-boy, Michael Phelps, learn some Mandarin RIGHT HERE - we just think it would show off the product better. It seems like an obvious method to display its effectiveness.