Here's an 'independant journalist' who apparently got an interview with someone who involved with the new Smash game. Take it with a grain of salt, but if this stuff gets confirmed to be true in the future I'm adding this guy to my list of sources.

Nintendo Upcoming Game “Fun-Fact” Sheet « The Nintendrone

They talk about some other stuff first (Multiplayer in Super Mario Galaxy? Hmm...) then they get down to the smash talk.

Like roto mentioned, they said a long time ago that the main game won't use the motion sensors, and will be built around the Gamecube controller.

It's a pretty quick read, as they're set up as bullet points instead of paragraphs.