Pakidan, I think you've misinterpreted what Sony is trying to do.
MS and Sony are not trying to capture a meaningful part of the motion control market with these new devices. Sure, they wouldn't mind if every casual gamer decided that motion controlled games were much, much better in HD, but they don't think it's likely to happen.
This is just about building the brand. Remember the original XBox? MS didn't think for a minute that they would steal the console gaming market from Sony. The point was to lay the groundwork for a more serious attempt - the 360.
Consider the position that Sony (and MS) would be in at the start of the next generation if they didn't do something now. The Wii is enjoying PS1-level success (relative to the total size of the market) and the Wii 2 would be poised to enjoy PS2-level dominance. People who bought into the Wii would have absolutely no reason to think twice about the PS4 or XB3 - they're just the successors to systems that held absolutely no interest for them.
By building motion control mindshare now, they can credibly offer a Wii2-like experience in the next generation. They're not really advertising to new customers - they're advertising to people who already own the Wii. They're saying "please consider us next time".
I think most everyone here is familiar with the way the industry works, or at least with the maelstrom articles on gaming. Sony and MS know very well that continuing to retreat to more and more hardcore territory as the Wii creeps up from the casual side of things is ultimately self-defeating. If they want to stay in this for the long haul, they've got to compete now.