I can see the opposite of this being true with LED backlighting (where a portion of the backlight is turned off to make blacker blacks) or OLED where the individual pixel is not being turned on. For standard LCD screens with a CFL backlight (where the backlight is always on), I don't see this being true at all. If anything, for standard LCDs, screens with motion banner ads would consume more display energy as the LCD pixels would need energy to be constantly flipping to update the animation on the screen (so running an ad blocker could make you greener!)