As a would-be author, I can say without any doubt that characters and stories are the foundation of IP.
That said, I completely understand Miyamoto's attitude and why he would take this attitude. Gameplay may be secondary to IP, but it is the foundations for what makes a game enjoyable, and it's what separates Nintendo games from every other company in the video game industry. It's not IP in a legal sense, but it is certainly Nintendo's selling-point.
Nintendo is also quite conservative with their internal IP, though. Games like Mario burn me out after two or three games, and I can't touch the series for a while. Zelda's not as bad because releases are further apart, but basically Nintendo's business model requires constantly creating or purchasing new IP for their ecosystem. I can think of several things I think Nintendo should acquire to broaden their portfolio.







