Let's have a look then. The sales from the start of May 2010 until the start of November 2010, which is before NSMB Wii was bundled.
New Super Mario Bros. Wii - 2249k
Mario Kart Wii - 1232k
It's not just the bundle that has boosted New Super Mario Bros. Wii, it was selling nearly 2:1 before it as well. Now, granted, Mario Kart Wii has been out for ages longer. Let's compare to how Mario Kart Wii was doing in the same period in 2009.
Mario Kart Wii - 2606k
That's actually higher. And that's even considering Mario Kart Wii had been out for over a year at the start of the period, whereas New Super Mario Bros. Wii had only been out for 24 weeks. Let's compare the period of February 2009/2010 (2009 for MKWii, 2010 for NSMB Wii) to the start of November. Note that for this comparison, both have had only one holiday season, but MKWii has been out for 8 months longer
New Super Mario Bros. - 4595k
Mario Kart Wii - 4102k
These numbers make me suspect that while New Super Mario Bros. Wii had a bigger launch and immediate sales, Mario Kart Wii might have better legs. Let's have a look at how the comparison was just before the bundles started kicking in. October 2010 sales
New Super Mario Bros. Wii - 444k
Mario Kart Wii - 225k
So while Mario Kart Wii had better legs, it doesn't have enough better legs. New Super Mario Bros. Wii is still going to pass it at some point in Q3 next year, and I doubt NSMB Wii's sales will start dipping below Mario Kart Wii's sales anytime soon then. Maybe later in the generation, but too late.
They're definitely going to be closer than I expected, though. 30-35 for MKWii and 35-40 for NSMB Wii seems fairer than my previous suggestion.
And looking further at it, Wii Sports Resort is definitely going to outsell both.
