> I don't think waterfall is actually used in other disciplines, perhaps we were just cargo culting back then?

I think this is half right. There was quite a bit of cargo-culting going on. But the fundamental error was to try to apply the project-management process for the construction of other kinds of artefacts to the design of software. I wrote about this very topic here:

http://www.zerobanana.com/essays/reclaiming-software-enginee...

You're correct that no other engineering discipline attempts to use waterfall-style project management of its design process. They don't really use it in the construction process either (in practice, design tends to continue alongside construction), though it probably has at least been attempted.

It was no surprise to see that the authors of this piece are in fact among the originators of the Rational Unified Process. They claim to have corrected their mistake; in fact they are still pushing the same wrongheaded ideas as they were in the 1980s.