New Super Mario Bros. Wii arcade machine isn't what you think it is. The Mario Bros. cabinet is actually a "medal game" -- in other words, it's a series of Mario-related mini-games (slot machines and the like) that can earn players more medals (i.e. tokens). According to Siliconera, players that reach Bowser in the up-to-four-player game have a shot at winning a jackpot.
Check out a video of the game in action on the official site (click 映像紹介 at the bottom of the page).