The plasma numbers are not what you would typically see.
Cnet tested out of the box with brightness and contrast turned up high (torch mode to use the parlance) then said you can save power by turning it down.

If you adjust the settings either professionally or even by yourself to levels that give you the right fleshtones and colors etc then you will find that plasma consumption numbers are about a fifth to a quarter of the stated numbers. The power consumption varies constantly with scene brightness and areas of brightness unlike LCD where the back light stays constant all the time.

More here:

http://archive2.avsforum.com/avs-vb/showthread.php?t=582016&page=1&pp=30