Having wifi capable DS with ability to purchase games via some NintendoApp Store would significantly reduce games cost, since physical cartridge, box and game manuals are no longer required.
And, knowing them, it'll be the same stale list of 1st party Mario games, Tetris, bad EA ports, and flash or iPhone powerhouse game du jour all for the low, low price of $15 a game, a savings of $10 over cartridges. Break out the noisemakers, what a savings!