Once upon a time, in a kingdom, not really far away, there was an evil queen. Her name was NSObject. To look nice, she was giving to her people lots of gifts. But the biggest treasure she was offering them was code reuse.
The RS letters are often used in the car industry to refer to the most powerful version of a given car. For MVC-RS, the same idea applies: it is MVC, but way more powerful, thanks to the 2 extra layers: Router and Storage.