Shoulder pain may be the gamers' new carpal tunnel syndrome as far as Wii's motion-based gameplay is concerned.
I think this was meant as a joke, but based on limited knowledge of typing style injuries, I believe that the Wii controller will be much less prone to repetetive stress injuries. With a normal controller, your hands are brought together and you are doing the exact same motion over and over. With the Wii, your hands are free of each other and swithing in a much less restricted way.
So even if a did require big movements (which they don't), the most you would probably see is tired muscles, not actually injury.