According to sales-tracking website VGChartz.com, the Wii's stellar holiday performance has pushed Wii Sports atop the all-time best-selling videogame chart. The NPD has yet to announce this fact, nor has Nintendo itself. The title, which has been bundled with every new Wii console outside of Japan and Korea, has sold well over 40 million copies (including non-bundled versions sold in the aforementioned countries). The previous number one title was another Nintendo-bundled title--Super Mario Bros., which was included with the NES for many early years of the system's lifespan.
Like Super Mario Bros., Wii Sports comes under scrutiny because the majority of the game's sales came because customers purchased it with the console. According to Wikipedia, the best selling games sold outside of bundles are Pokemon Red/Blue and Nintendogs, both of which were sold with multiple versions. Super Mario Bros. 3 is the top selling title to be sold by itself. Regardless, with the popularity of the Wii with casual gamers, the argument can be made that Wii Sports is every bit as influential as those two megahits.