That's true! On the Mac there's only one glass pane (the other half is the chassis/keyboard), so my idea was that the lid is just a kind of window into a fourth-dimensional space where the actual screen lives. When you open the lid, you're moving it closer to this "ethereal" screen until the two attach. As you close it, the screen stays fixed in that "virtual" space, so the angled glass distorts the light.

I'm aware it may not make sense physics-wise, eh. :)