Here's a news that I got from getting information for the upcoming game Guitar Hero: On Tour. Vicarious Visions, the developer for the said game for the DS has mentioned they tackled lots of challenges before coming up with the game.
Obvious reasons is the DS itself. Too keep to the DS being compact, they rejected the fact of making the peripheral look like a guitar fretboard. That means, no guitar sized thingy.
The most interesting thing I found was about Vicarious Visions asking for permission to add buttons instead of mapping together with the buttons available on the DS. That means the buttons that is shipped with Guitar Hero are additional buttons for the DS.
Very interesting sales strategy.