We wanted to be able to leverage that network connection with all three of the [Super Mario Run] modes to keep all of the modes functioning together and offering the game in a way that keeps the software secure. This is something that we want to continue to work on as we continue to develop the game.
But actually, the security element is one of the reasons that we decided to go with iPhone and iOS first. So this is just — based on the current development environment — a requirement that's been built into the game to support security and the fact that the three different modes are connecting to the network and interacting with one another.
Miyamoto notes that at one time they thought of having the World Tour [story] mode available to play offline; however, when operating in standalone mode it complicates the connection back to the Toad Rally and Kingdom modes. "Because those two modes are relying on the network save, we had to integrate the World Tour mode as well."
Super Mario Run will be released on December 15th but you can already visit an Apple Store to demo it now.