Pokémon is the king of promotion, and they go a long way when it comes to attracting buyers. You see McDonald's toys featuring your favorite monsters and are immediately reminded of the games, series, comics, or other media. What if you don't have one? Maybe your system was lost or you sold it. Great excuse to go out and get a new one while you're thinking about it, right? You'll probably pick up a new Pokémon title while you're at it too, and before you know it you've bolstered sales, even just by a little bit. Think about that effect multiplied all over the world, and you've got an idea of how the series can help keep handhelds afloat.