I think Miyamoto got it down. Nintendo has always been really user centered in the design of their hardware and software. Just look at the interfaces they put out. Always very user-friendly, efficient, easy to pick-up and understand. There are not a whole lot of other developers who can rival them in this. This is cleary one of their strongest points, putting out user friendly interfaces. And even while their controllers might not always have been the very best in ergonomics for all people and not suited to all genres equally well, they always put out some really user centered designs.
The natural look of their D-pad, the well hidden and quite functional shoulder buttons, different colored actionbuttons so people can seperate them faster, analog sticks for easier and more accurate 3D movement (they weren't the first with this, but they were the first to implement it correctly), user feedback to the user through rumble, wireless controllers for more freedom and no cable clutter. Hell, even their less succesful attempts where really user centered in design like their asynchronous button layout on the GCN controller (again, so ppl can seperate them better) and the trigger on the backside of the N64 controller.
Now they take it a step further with the RevCon by replacing many button pressed functions with more natural movements by hand or arm. They even effectively replace the 2D control peripherals (analog sticks, mice, D-pads) with a 3D control peripheral, so as to better suit to 3D interfaces and interactions which games arguably use the most out of any computer application. Third important point in case is of course the look of the controller. They lower the threshold to pick it up for a lot of consumers (mainly people with little to no game experience), by making the controller look like a remote since people are much more used to that look. Also, because they replace most buttons with movements, they don't need many buttons on the controller, which makes consumers feel even more comfortable. Oh, and don't forget you can hold it with just one hand instead of two. Another thing which makes people feel more comfortable to pickup and use it. More experienced players will of course buy more complex and traditional games which require the analog stick attachment.
For someone like me who is studying in a field about human-machine interaction and making consumer products as user friendly and user centered as possible, this whole controller idea is something truly amazing. It has A LOT of potential and possibilities and I just hope they pull it off well. If their success with the NDS and their past experiences with these kinds of things are any indication though, this shouldn't pose a big problem. Just can't wait for demo's of real games being controlled by this thing.
Just think about it. Potentionally (keyword) the controller can make games:
a) more immersive because of the movement based controls and the fact you hold it with just one hand and it's light in weight (which gives you less of an idea you are actually holding a peripheral in your hand to control the game)
b) more user friendly to a much wider audience than previously because you only have to hold it in one hand, there aren't many buttons present, the controller has a natural look to it and many actions can be performed by natural movements
Still, the games have to be designed in such a way as well, as the NDS has perfectly demonstrated.