ergophobe - 9:34 pm on Mar 4, 2008 (gmt 0)

Because of the way GIF compression works, repeated pixels of the same color (in this case white), especially on the horizontal axis, add very little to the file size. Try making a monochromatic white image 1px wide x 10px long. Now make it 1000px long. How big is it? 100 times as big? Nope.

I get 44 bytes for the 10px image and 71 bytes for the 1000px image using PS CS3 Export.