[rwallace]

Safety critical software projects do have levels of completeness and rigor comparable to civil engineering. An example is the space shuttle control software, which ran for decades without a single serious failure - by contrast, the shuttle hardware in the same time period suffered two lethal failures.

The price paid for that, of course, is levels of cost and bureaucracy comparable to civil engineering. Try to build a website for a startup that way and you'll be out of business long before you ship anything. The correct level of rigor depends on what you're doing.