My own thoughts are that the screen is grey to speed up screen refresh and save power.
To go from white to black you have to move all the ink capsules. Max time, max power (the ink capsules are migrated by electrons, the more you move, the more electrons you need.)
To go from grey to black or from grey to white you need to move half the ink capsules.
One of the key features in the iLiad appears to be the +/- 15V swing they can apply to the electrophoretic manipulation of the e-unk panel. The larger the voltage, the quicker the ink can be moved. This appears to be courtesy of the new version of the driver chip they had developed.
My guess would be that if you pop the top on the new Sony Reader you'll find this chip in it as well (when/if it ships.)
Some of the failures reported in the iLiad panels could be due to them needing to spend more time getting the tolerances in the printing process used for creating the panel under more tight control. At 30V even smaller variations in line width in drawing conductors on the panel can result in electrical shorts.
One of the issues holding back Sony could be the need to increase the panel yield ratio. So far iRex seems willing to let customers handle the final panel inspection.
