Sigh.
Again, songs aren't the property of Nintendo, MS or Sony so NBGI can do what they want with them, a game being licensed doesn't mean that NBGI gave away their (intellectual) property away to a third party.
A game license isn't much more than a moneyhogging approval that the contents of a game is deemed suitable for the target system by the licenser.
Also, unless someone proves me wrong, iM@S DS doesn't have the capabilities for 'real' DLC, though it does have unlockables.