pilot_nate :
Also, out of curiosity, why do they use a 16:10 aspect ratio?
Apple's core client base is graphics artists, photographers, and video/audio editors. A 16:10 aspect ratio allows you to edit 16:9 video while still having editing controls visible along the bottom. Although the MBA isn't aimed at these clients, they're probably aiming for consistency among their products' appearance. So they all carry the 16:10 aspect ratio.
Also, the closer you are to 1:1 aspect ratio for the chassis, the greater the ratio of enclosed volume to surrounding surface area. So for the same internal volume, a 16:10 laptop will weigh less than a 16:9 laptop because you need less metal for the case. That was probably a major factor for the MBA.