URLs are supposed to be atomic; there's no guarantee that truncating a url is going to lead you anyplace useful. The fact that it often does started as an accid

URLs are supposed to be atomic; there's no guarantee that truncating a url is going to lead you anyplace useful. The fact that it often does started as an accident of early implementations (hey, show a directory listing by default) followed by a security backfill (damn, directory is showing; better drop an index.html in there) which lead to a convention (better put something meaningful at each level of the url, because people will try them and we don't want 404 errors.) I don't think the convention can be assumed to be true for any website to the degree needed to implement a feature like you suggest. There would be too many errors when people click on those buttons, and people would blame the browser, not the website.