It is not completely accurate to compare the sells of this to that of a Super Mario on the GameCube, but to instead use a variety of selling numbers for the past few Super Mario games such as the recent one on the DS. Even though the New Super Mario Bros. game is a bit different type of a Super Mario game than Super Mario Galaxy, if you look at the numbers it sold on a game system that has a similar diversified audience as the Wii will most likely have, then a Mario game more directed towards more hardcore gamers can still thrive on a console with a wider audience and sell well. Not to mention the fact that Super Mario Sunshine was a game that was not as highly rated at the time as like when Super Mario 64 came out, so Galaxy being a more highly thought of title than Sunshine already, would be a better seller than Sunshine. Also, the more mainstream audience the Wii is going after is composed of many people who know who Mario is (since so many people do) or even have experience some of the Mario games in their past. This makes the mainstream audience for the Wii more willing to buy a more "gamer" game with Mario in it - leading to higher sells.
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