It doesn't matter how Nintendo code their games. As I said, it's compiled and broken down into machine language anyway.
Nothing, in any form of code and be added too, once compiled.
No game can be developed to accept new DLC; the content (items or whatever) simply HAS to be in the game from the very beginning. There's no "probably" about it.
For example, if Nintendo decided they wanted to add a piece of furniture as new DLC next year, they couldn't.
Programs like Rockband and Guitar Hero work differently. They have an algorithm embedded in a section of code that converts new data into usable content. ie. there are only so many notes, durations and instruments etc that are possible. An algorithm simply breaks down a new songs data and converts it into playable notes etc. There are no animation changes, no new icons or graphics; nothing is physically added to the game, it simply converts an audio format to a playable format which calls their existing notes "in-game" and than calls the track to be played from the hard drive during playback.
