This is seriously mind-blowing to watch and Thain and I had our jaws dropped the entire time. Not only does this designer get his iOS 7 mock-up razor close to the actual thing, but he does it using only Microsoft word and no outside assets. Only text, shapes, gradients and special characters. This is a clear demonstration of how a good designer can put any tool at their mercy to get a job done.
Now, we have to remember that the work it takes to conceptualize a mobile operating system's visuals goes much deeper and it takes years. The key thing here is this - A truly great designer isn't bound by what's available. They can use anything to evoke a response, and in this case it was Microsoft word. It's the same thing as watching a street artist make a beautiful painting from old spray paint on a dirty canvas. It's a flawless execution that makes this awesome!