If, for example, some pad was an inch-wide and with 1000 dpi resolution, then it couldn't ever be configured to cover a 2000 pixel wide screen that way - we don't know the specs of the controller elements yet.
With some acceleration it could - finer control with small movements, but quick movements provide more travel. Not sure how well this would work, but I like Apple's implementation on their trackpad (I realise I may be in the minority here!).
