Mario Party games, those part games featuring... Mario, aren't actually made by Nintendo. They are made by Hudson Soft. And it's no wonder they are similar to the newly released Wii Party.
Nintendo has a long history with Hudson, going back to the Nintendo Entertainment System days, releasing games like Bomberman. In 1998, Nintendo and Hudson created a subsidiary with the aim of creating Nintendo 64 and Game Boy titles. The Sapporo game company has since been purchased by Konami and is now based out of Tokyo.
After Hudson developed Mario Party 8, several key designers left Hudson and went to work for Nintendo subsidiary Nd Cube, which developed Wii Party. Nintendo owns 96 percent of Nd Cube, which has offices in both Tokyo and Sapporo.
Nintendo created Nd Cube with ad agency Dentsu in 2000, and it has developed games like F-Zero: Maximum Velocity.
So think of Wii Party as the spiritual successor to Mario Party, just minus the Mario bit.