I'd be willing to bet they are using the same blow out device designed for surface or "shallow" well operation; between the external pressures found at ocean depths of 5000ft (2,500 psi) and the well's pressure (9,000 psi)I'm not suprised it failed. Interesting point: they aren't even showing us what the big leak atop the blow-out prevention device looks like. just the smaller one on the cameras.