Ok, now I understand what you are saying. I've built systems like the one you've described. The difference you'll find with one of the other CMS packages (Drupal, Joomla, WP, etc...) is that the pages are not physical files that you create with content management regions in them, they are held in the database as data and when called from the CMS, they assemble using a templating (or theming) system to render with all of the design elements.
In really simple terms if you create a page in one of those CMS's, the data that you create will include: the content ID, a title, the body text and information about where it fits in the navigation. When it's saved it automatically adds a link to your navigation and when you click the link, the data for the content ID you clicked gets pulled out of the database with all the right bits of associated data and then fills the template that you have created for it. This means that you create one physical design template and can create infinite pages, sections and subsections of pages in the database.
You can configure a CMS to associate other information with a page by adding custom fields or taxonomy so that you can make pages fit into categories or groups and then use your theme or template system to treat pages differently with maybe a different layout or visual treatment if they have a specific custom setting. There is a lot you can do with template systems in these CMS's.
I hope that made sense.