Maybe it was to preserve battery life, but there’s no backlit keyboard on the new MacBook Airs. I think that’s a mistake on Apple’s part.
I’ve always found the backlit keyboard one of the most useful feature on the Apple laptops I’ve purchased. Apparently, I’m not the only one who thinks so. You can check out a thread on the Apple Forums about the lack of a backlit keyboard: http://discussions.apple.com/thread.jspa?threadID=2620491&tstart=0 .
If you want to let Apple know that the new MacBook Air needs a backlit keyboard, you can fill out a form at http://www.apple.com/feedback/macbookair.html on this and other comments on the MacBook Air.