Oh yeah, in Others NSMBW sold about 300k first week but no one is calling it a flop. Some people really don't want the Wii to succeed in Japan it seems...
Try comparing the DS at the time when NSMB DS released and the Wii right now would you?
The point is the same. It kept selling as well as it did because the console userbase is greater than the PS2 and continues to grow. The Wii will never be that.
We're talking about FW here...
LTD, why would something like that matter? Have you seen MK DS and MK Wii sales?
MK DS: 16.26m
MK Wii: 18.60m
Then have you compared FW sales for NSMB Wii and DS? NA FW for NSMB DS it sold 171k, NSMB Wii sold 952k. In Others it sold 131k FW week and 297k FW for NSMB Wii.
You suddenly think a game like Mario, being 2D (first one in 15 years), with the Wii's profound legs, and the fact that the Wii is still selling loads (and is still on track to beat the PS2), with the inclusion of multiplayer (big feature among casuals, with the DS you can't have it the same. Does NSMB DS even have multiplayer to begin with though?) and one of the best games on the Wii so far it won't reach similar numbers? And this isn't the first case either like I said with MK Wii.
Edit: If you're talking about JP only though, we'll have to see. I wouldn't put it past NSMBW to sell millions too. Not necessrily 5-6 mil, but at least 3 mil.