Interesting, but so far, the option to go for a 3DS just for Dream Radar or the Pokedex Pro doesn't seem worth it, so they're losing money by not giving a choice for the two systems.
It doesn't seem to be too much of an issue to adapt between systems, look at the Legend of Zelda: Twilight Princess. You can play it on Gamecube, or its upgrade, the Wii. So, why couldn't they do it for Black 2 and White 2?
And then you get to the Walmart promotion.