Has anyone looked at the Macbook Air pics on the banner? It appears that they might be the new version. Look at the screens... they appear (at least to me) to be wider than the keyboard nearest the hinge. This could imply that the screen size has increased on the new laptops.
Looking at Apples website, the pictures of the Air show the current gen screens are the same width as the keyboard.
Here's the exact picture you are questioning on the banner- it's already on Apple's Lion website of the current 13" Air. No difference in screen size.
http://www.apple.com/macosx/what-is/