ChartTrack UK states that Mario Kart for the Nintendo Wii is:
Far and away the biggest launch of any Nintendo published title.
The 8th biggest launch week in UK history, the Mario Kart launch was a bigger launch week than all 5 other Mario Wii games combined. Mario and Sonic at the Olympic Games, Super Mario Galaxy, Mario Strikers, Mario Party 8 and Super Paper Mario were toast in the eyes of Mario Kart. Looks like the longs will be longer now, and the UK sure as fuck loves racing games. Especially one that involves plumbers.