Yes, I'm talking about Japan only. NSMB Wii selling 3 million would prove my point though. It's not about it flopping or selling badly, but let's not compare the DS and Wii when talking about Japan.
Also, it isn't the first 2D mario in 15 years. It's only been 4 since NSMB DS.
Lastly, legs aren't about a platform, but the type of game and appeal it has. RPGs, regardless of system or console, will be frontloaded. Pokemon would still sell gazillions on PSP, etc.