I like to think that people writing actual mission critical software try their absolute best to get it right before shipping.

People try, but the only fundamentally different part is that you spend time thinking about and documenting your process rather than just doing it. There's always one more bug. Usually there ends up being a human covering up for the system's failures somewhere that no one else notices. That's the driver in the car, or the factory tech who adjusts things just a bit.