I call BS only because, giving Microsoft the benefit of the doubt, I would think they were smart enough to know that the only reason the Wii remote succeeded was because it came with every Wii console that was sold since it launched. As a Gamecube peripheral, the concept would have failed miserably. As an Xbox 360 peripheral, I would expect the same.
Companies have modified controllers in the past. Microsoft did it with the Type S Xbox controller and Sony is doing it right now with the Dual Shock 3 (having previously done so twice with the PS1). That's not the same as asking your own userbase to adopt a completely new controller when the old one isn't broken.