[PaulHoule]

A lot of it is that consistently people design things on the assumption that 80% of labor will be in the first release, rather than the 80% going into maintaiance which is what happens most of the time.

This is closely linked to the idea that least cost development is a matter of doing every individual action 'cheaply' and pretending you are not going to screw things up. If you want least cost actually least risk is a good approximation.