Website admin skins/themes clearly have a big market. Just see many different options for Drupal hosted on drupal.org or some nice commercial ones on themeforest.net (not Drupal specific). Administration themes are great when you'd like to separate your administration interface from your front-end. And several Drupal studies showed that many people need this separation to understand where content is managed and what does everybody else see of the site. Of course your mileage may vary and there are all kinds of sites where community participation is on a level that admin/front end separation is meaningless. The point of this blog post is not even administration themes, so let's shelve that discussion.
Websites often replace traditional web applications as well, when the "front end" of the website is already some kind of data input / management UI, where the data is usually not in the form of textual posts with comments tagged by topics. Navigation is not primarily search based because pages for different functionality in the site are not searchable in a traditional sense. Finally, menus are not built by the site builders but rather the application author, putting in menus and navigational elements via code suited for the application.
In Drupal, this kind of theming needs a different approach compared to traditional admin themes, because the web application will most probably not offer the usual Drupal admin functions. For this role, a theme more like the general ones of themeforest's admin looks fits more.