I was about to argue that this website is actually an excellent example of what you seek -- each link has a separate URL associated with it that returns a page containing that content. The links point to these real URLs so they work with "open in new tab" and "copy link" and in browsers without JavaScript enabled, while the JavaScript that runs when you click it changes the page content via AJAX (possibly saving a few round-trips) and updates the current page URL so that back/forward history and the address bar both work just like you're navigating between real webpages.
And this works perfectly in Firefox (with JavaScript) and almost perfectly in Lynx (the table of contents still fills the first screenful, but that's hard to fix since Lynx doesn't support CSS). But it completely fails if you have JavaScript disabled in Firefox.
Every page starts with the table of contents visible and the content collapsed (through CSS). The page then seems to assume that JavaScript will be able to immediately switch the page to the correct view (i.e. the site is broken if you have working CSS but not JavaScript). Navigation to a given page directly should start the other way by default, and to make that happen is just 21 missing characters (` class="page-feature"` on the <body> tag). However, this unfortunate error completely ruins this otherwise beautiful example of progressive enhancement.