Ah ha. This video by Max Rudberg (the same Max who posted the Multitasking Tray gesture video) demonstrates almost exactly what I was talking about in my last link about the Notification Center being “above” the Home screen rather than “under” it.
In his description of the video, Max also hits on exactly what my gripe is:
The linen texture has been used to denote that something is at the very bottom layer of the interface. For example, when you open a folder, the wallpaper separates to reveal the folder contents on a linen texture. Therefore, the Notification Center that slides out above the interface shouldn’t really use the linen texture.
Though I’m not sure I like the way the Max animates the whole Home screen “falling” and bouncing to the bottom of the screen, I do like the idea of the Home screen sliding down to reveal the Notification Center underneath.