BP is supposed to be one of the better players in the industry in terms of safety (been in contact with a few friends). They didn't even own the rig that was drilling the well and the main fault is that the main failsafe, BOP, that was supposed to shut the well in event of trouble didn't. It also didn't shut manually when the rig operators tried as they were evacuating after the explosion. It also didn't activate when the remote vehicles tried to engage the valves directly on it.
Of course the guys that made the BOP are the leaders in the industry and even invented the first ones way back when. It might have been human error, but the story isn't that simple.