When trying to persuade people not to overload their navigation menus, I have often drawn an analogy with road signs. These must be a model of brevity, because drivers need to be able to digest them quickly.
Web users may not be travelling at 60mph, but they still want to get their stuff done quickly.
I enjoyed this Gerry McGovern article that draws a similar analogy:
The core purpose of navigation is to help you move forward. Designing digital navigation is not that different from designing navigation for a road. You always want to be able to help people maintain their momentum and get to their destination as quickly as possible. The essence of momentum is to help people move forward, and this is the essential purpose of navigation—to help people move forward.