You need a nunchuk for for most games. And I have no problem with that (I think the nunchuk is probably the most comfortable "left half" of a controller I've used), but I think Sony/MS have a chance to improve on the concept, or at least to differentiate their product from Nintendo's.
As for the wiimote's 3D position sensing, it has a lot of problems. There's no way for the system to know where the remote is in absolute space, e.g. on the left or right side of your body. Even if it could work from an absolute starting point (like by pointing the remote at an LED cluster), it would quickly lose its place after turning away from the screen because the accelerometers are simply not accurate enough. And the remote's tilt sensing works pretty well on planes it can measure against the direction of gravity, but it's almost completely incapable of detecting rotation along the horizontal axis.
That's why a camera-based system, which could tell the precise location and orientation of the controller, would be an even bigger leap over the wiimote than the wiimote was over traditional controllers.
If you ask me both ways are a waste of time, would you rather them have their first string team (like the God of War team) create a casual friendly game to attract an expanded audience (that might not work), or do you want God of War 3?
It doesn't have to be either/or. Done properly, support for the motion controls (and more importantly, the pointer function) could be cleanly added in on top of the existing games.
And don't make the mistake that motion controls = casual. There's huge potential within hardcore games as well.