Mario Kart

The decision to title the latest 3DS incarnation of the Mario Kart series Mario Kart 7 may seem an odd choice at first, especially considering that there is no game titled Mario Kart 6. Or Mario Karts 2 through 5, for that matter. No, the previous titles all forewent the number system for their own unique sub-titles, such as Double Dash and Super Circuit, or simply specifying what system the title appears on, like Mario Kart 64.

So why the decision to implement a numbering scheme for a series that, until now, has never seen one?

Judging from the game itself I'd assume that it's