It's mostly about the way permissions are handled. User-oriented permissions are about protecting the system from the user. This is a useful notion when people connect to a multiuser server via a terminal, or for shared network resources, but is nigh useless and generally just gets in the way for personal computing devices.
The mobile OSs orient the permissions system around the applications, protecting the user's data and resources.
That's fair enough although one of the reasons that works is that applications are sandboxed and limited in terms of what they are allowed to do. Certainly one could imagine a tablet/phone OS that was more oriented to desktop use cases (mouse support, etc.). But now we're back to Windows 8 and possibly Surface Pros and that just hasn't been a particularly popular model.
But that's exactly what we want: applications that are only allowed to access what the user has permitted them to access. And I believe it can be done better than popping up a dialog all the time like UAC or just once at first launch like Android/iOS.
You don't need to tabletize your interface to implement this concept. Bubblewrap, FireJail, and some similar software already exists that implements this in Linux (poorly in my opinion, but it works).
The mobile OSs orient the permissions system around the applications, protecting the user's data and resources.