Bad analogy. Seat belts are a marginal expense on a car (I have a hard time believing that they would even add $500 (3%) to the cost of a $15,000 car). The reason that so much current software is so shoddy is because doing it Right would increase the cost of development substantially. Add insurance, bonding, auditing, and other methods of protecting against the possibility (certainty) that a bug slipped past QA on top of that, and you're looking at software production costs increasing by an order of magnitude or so. And that's probably optimistic.