I think you're oversimplifying it a bit. It is more than just fixing a leaky pipe. Due to the fact that it is under water. The water causes tremendous pressure at that depth, and the oil squirting from under the sea floor is under even more pressure. So, IMO, a better analogy would be trying to fix a hole in a submerged submarine from the inside.
That, however, does not negate that fact that BP seriously screwed everyone with that pipe.