And there's the flaw with this comparison. Sony is not comparing the PSP Go to a DS. It's probably more in line with a ipod touch, if anything.
The DS is what you buy your kids. The PSP Go is what you buy yourself.
It doesn't feel natural to me to use a mouse to control and fire a firearm, or a sword and besides, I sit at a chair and push a mouse around all day at work (and sometimes longer) --- it's not something I want to do for leisure.
And there we have it. The control mechanism needs to be suited to the game you're playing - so generally FPS games are most accurate with mouse & keyboard. Generally platformers work best with a joypad. I'd argue arcade driving games also work best with joypad. Driving simulators work best with a steering wheel with force-feedback.
Waggling some nintendo remote in mid-air doesn't feel natural to control a steering wheel either, and it's not accurate, nor realistic.
The problem isn't the controller, it's the game. Boom Blocks would be stupid with a keyboard or joypad, for example. A new control scheme requires the game producers to see it's value and design the game accordingly.
I didn't do it! Nobody saw me do it! Can't prove anything! -- Bart Simpson