In the followup comments, "Bob" says that he isn't sure if an X-ray of a MacBook Air would breach national security, but that someone would come along shortly to determine whether it is or isn't. Link (Thanks, Phil!)
After hearing stories of trouble at airport security checkpoints related to Apple's newest laptop, TSA acquired one and x-rayed it. The TSA's "Blogger Bob" summarized that because the MacBook Air uses a solid state drive instead of a traditional hard drive, its internals look entirely different than any other laptop.
He also says that he cannot show the image of the x-ray of this laptop because that is sensitive information.
I'd love to see some rebellious x-ray technician pick up the slack and show us all what's so special.