In part, that's because the Gaze UI now supports keyboard input, whereas last year it was completely touchpad-based (and we all know touchpads aren't the most reliable things even under normal circumstances).

ENGADGET: Hands-on with Tobii REX, a peripheral that brings eye-tracking to any Windows 8 PC (video)

The other is that the method of input is different, because there is either only a tiny keyboard or none at all.

ECONOMIST: Metaphorically speaking