Even though the 3DS and DS are about Neck and neck with hardware sales, the 3DS is behind by 25 million in software!

[Soundwave]

The two Brain Training games sold like 35 million copies.

Nintendogs sold 20 million copies.

These brought in blue-ocean/casual shoppers which also probably helped NSMB and Mario Kart.

Not rocket science that the bulk of this audience moved on to cell phones. Brain Training/Nintendogs was a bubble, and like all bubbles, it was going to pop, and it has.