Regardless of what MS say which I believe is a poor way of promoting Natal and not something they believe, traditional controllers are here to stay and I doubt anything will change that.
That said motion controls are here to stay as well but in a lesser capacity. Eventually we'll see a combination of Natal and Wiimote/nunchucks, though the mote/chucks could be anything as long as it's something for your hands, for motion controls but that soon.
Devs and the console manufacturers are in the infancy of motion controls and just figuring out how they should be used. They have their own controllers and will be trying to sell them first to their established userbase. Trying to have their games incorporate their motion controller.
Down the line they will all 'borrow' each others ideas and we'll have a standard for motion controls. Look at joypads. All have rumble (finally), shoulder buttons, two thumbsticks. It took a while for that to be the standard.