“When you launch an app on your mobile device, the device essentially becomes that app.” via Max Rudberg – ✎ Flat UI is not the only way forward
This is a great, keen observation, and it correlates to why having clean, minimalist design makes a lot of sense for the hardware of mobile devices. These are windows onto many worlds. As such, for them to blend away into near invisibility is precisely what they should do–so that you can immerse yourself in any one of those worlds without distractions from the window itself. The more invisible the window, the better.
But for the world experienced through the window, it would be as if you were forced to live in Flatland, if you were limited to flat, minimalist design. Even though it is a deception, it is a beautiful deception for a piece of software to make you truly feel you are a part of the story it is telling, the story it is helping you to become a part of.