To me an arcade game is something that requires no tutorial level, no instruction manual, no prior knowledge, and no introductory cinematic sequence. You turn it on and already know how to play.
Wii Sports has 2 things in common with Pac-Man (or Pong for that matter): ZERO BUTTONS, and one of the most famous games ever created. You might even say the Pac-Man Fever of yesteryear has come back as Wii Sports Fever, but sadly nobody's written a song about it yet.