I'm not Mike, but I'll try to respond here...
Plasma displays have (for lack of a better description) swirly, unstable pixels. Looks stable from a distance, but if you put your eye right up to the panel you'll see what I'm talking about.
A contact probe with a small aperture like the i1 display will give different readings each time it samples a pixel. Therefore it is necessary to sample the color and luminance from a distance to get accurate, useful readings.
Examples of non-contact probes are x-rite Hubble, Konica-Minolta CP-200, Orb-Optronix SP100, Photo Research PR-655, etc...
All of the devices I've listed are extremely accurate and useful for profiling plasma displays as well as projectors.