I'm going to have to lean to Nintendo on this. I think both MS and Sony are going to look at the Wii's success, and try to add (better) motion to their controllers. Nintendo, expecting this, finds something else to add in addition to motion to their controls, allowing them to stay in the lead for the next generation. Maybe a touch screen on the controller...?
However, I'll even go so far out as to say the following gen will be Microsoft's. Nintendo, in a rush to add features, makes their gen-9 controller too complex for the "casual", resulting in losing the lead to Microsoft, who, still not having made back all their $9 billion in losses, makes something simple, and swipes the lead from the N.