This idea fails even on its own, since it presumes that URLs have structure, even within a particular site. So if you want to add a new page, even a one-off for a special occasion, then you have to start thinking about where it fits in your ad hoc URL/navigation scheme, too. Also, if you want to redesign navigation, you have to change all your URLs. URLs are brilliant because they are separate from navigation; that's a feature, not a bug.
But it's also philosophically wrong. The URL -- a simple string that can be used to fetch any resource -- is the single greatest innovation of the web. A simple string can pass through literally any human communication system. Speech, print, text messaging, anything. A URL is not an inherently intuitive concept so it is not all that usable. But it's necessary. Training users to recognize URLs is vitally important, or we are back to relying on AOL^H^H^HFacebook to provide navigation tools.