[exception]

Here's my first shot at a theory of how Pixel Sense might work

There is an IR LED backlight as well as the regular white backlight. They have an additional per-pixel LCD shutter that blocks IR. The display repeatedly displays sweeping horizontal and vertical patterns on the IR blocking shutters. At the edges of the display there are a series of IR light detectors. When an object is placed on the display, some IR light will bounce off the object and be internally reflected in the plane of the panel glass. The light is received by the detectors.

What think ye?