NPR writes about removing references to the world outside the screen in iOS 7.
While removing references to the world outside the screen seems like it a good idea, it doesn't always end up working.
Modern humans have been in existence for 200,000 years. Throughout those years, basic properties about the world we live in and physics have not changed. We have learned how to navigate the world fairly well. We've learned to read and interpret lots of visual cues to create a mental map of the world surrounding us. With a good mental map, we can figure out how things work. This is great! Without some visual cues (like shadows, perspective, relative size), it would be hard to navigate our world. For example, it would be very difficult to differentiate between a staircase and a ladder. Imagine walking up to a staircase, then moving your arms and legs vertically and failing to climb the stairs. How embarrassing and frustrating!
In iOS 7, a lot of those very basic visual cues we're used to are still there, and you might not even realize it. One that often goes unnoticed is occlusion. Occlusion says that elements that are "closer" to the viewer are visible and block out (or obscure) elements behind it. It seems so trivial. iOS 7 still very much uses this principle. App icons appear over the wallpaper, App icons appear on top of the dock, alerts appear above apps, and the list goes on and on. We rely on these cues a lot more than most people realize. So much about our environment can be learned just by these cues. iOS 7 even adds some cues like parallax to the OS to give a slight hint at depth in the OS. This stuff is great! It won't be consciously recognised by a lot of users, but it will add to the feeling of depth and vitality in the OS.
NPR writes that shadows have been removed from the OS because they're no longer necessary in this new digital world.
If you look at the buttons on the keyboard you'll see that they are very subtly three-dimensional. They even cast a shadow that you can see, if you look closely. And they're rendered with a fictional light source that hangs above the gadget itself.
In previous versions of iOS, shadows were used to hint at depth. The keys were on top of the keyboard frame. If the light source from above the device was removed, then why are there still shadows? Yes, in iOS 7, there are still shadows below the keys.
However, instead of the soft shadows (light diffuses over distance) on previous versions, the shadows are sharp and just vertically offset 2px (1pt). This is something you would not see in nature, and is confusing. Now it doesn't seem like a shadow on the keys and looks like the keys are now lined with a thin bottom stroke or are sitting on some short of shelf or container. It's ambiguous. The entire point of those shadows has been lost and instead of being informative (visual cue for depth), the new design is now inaccurate, and confusing.
Shadows still exist in iOS in some places. Some of the best examples are in seen in sliders (the thumb has a shadow to suggest it is above the track and can be moved), and switches (similar to a slider, but only has two possible states: off/on). This is incredibly important! These are subtle hints at how to interact with UI controls that appear across so many apps. Shadows are also present in view controller animations, Passbook passes (app and icon), Camera app icon (inner shadow on the glyph), Settings app icon (inner shadow on glyph), below the yellow header in the Notes app icon, below the Video app icon's black and white clapper board, on the tabs in the Contacts icon and more.
So has the lighting source on iOS 7 really changed? It doesn't seem so.
Has the way humans physically see the world and create mental maps of objects in their environments suddenly changed overnight after being roughly the same for 200,000 years? No.
Yes, I realize people with very poor eyesight or none at all have also been able to survive, too. There have been great technical improvements in iOS 7. A lot of the design changes shouldn't negatively affect those without sight. The technical improvements should benefit all users.
All information in the article regarding iOS 7 is publicly available and was presented in the WWDC Keynote or on Apple's website.