I don't know if it is an issue or not, so I post here first.
In offical theme, with contat.php and register.php, there is a 404 page if relevant plugins are not enabled.
why the same behavior is not the same with news.php, pages.php, favorites.php and slideshow.php, if relevant plugins are not enabled?
there is the same question with search page. this is not a plugin but you may disable search in theme options, but you can access to the page in front end (with the right url in the browser).