Nintendo's handhelds have a cheeky little sideline in multiple versions of borderline identical games. Popularized by Pokemon, it's not uncommon to see a DS title coming in two flavors. Nintendogs pushes it with three, but apparently, Shigeru Miyamoto wanted fifteen at one time.
The iconic game designer wanted to recreate a pet shop experience, where one would spend a long time trying to choose an animal. Sense prevailed, however, when Nintendo's sales team said it would be too difficult for retailers, and so instead the team went with three.
A Wii version of the title was also considered, but because of the distance between the Wii remote and the television, Miyamoto worried that "it might not have felt like you were petting your dog."
The man is frigging insane.
Iwata Asks: Nintendogs + Cats Edition [andriasang]