In his entry "Security Analogies are Usually Wrong, Michael Howard does a bit of delving into the "software security by analogy" poing of view:
I usually roll my eyes when I hear statements like, “If [bridges|cars|airplanes] were built like software then…” because comparing physical items and software is just wrong. They are not the same thing, you cannot compare them.
Anyway, it's worth reading since he makes a very humorous counter-analogy. Of course, the reason that I think this is particularly humorous is that the next thing I read after it was the coverage of Mary Ann at the WWW2006 show:
"What if civil engineers built bridges the way developers write code?" she asked. "What would happen is that you would get the blue bridge of death appearing on your highway in the morning."