I think it more just shows how important a strong brand is at selling games on the Wii - especially when it's something like Disney and Mickey Mouse that perfectly 'fits' the Wii's family appeal and is aimed perfectly at the Wii's younger audience. I can't honestly think of a brand that fits the Wii better in all honesty.
The games quality and marketing no doubt helped push things further, I don't want to try discredit that, but in all honesty you stick Disney / mickey mouse on the title and it's gonna sell on the Wii. Toy Story Mania was the bazzlionth Wii minigame collection, and despite being another derivative 'PARTY!' game, it sits at 1.3m worldwide, because it had the brand.