re: Huge difference
But commercial airliners are a mature technology. Few surprises are likely given that flight experience with jet transports go back to the 1940's. Planes like the Comet already paid he price for lack of experience.
By contrast Spaceshiptwo is a completely new vehicle, with only the few flights of spaceshipone as the experience curve. So there is a need for even more test flights then for a plane like the A380. Good thing that Branson has deep pockets. Very deep pockets.