Flat design, like everything, is just styling. Flat design owes more to the fact that brand new device touch-screen interfaces at first were fairly rudimentary, and no one really knew what to do. Typographic interfaces were the latest rage - and so there we are - flat as it gets. There’s no real improvement over past desktop design guides. It’s just different. It’ll pass, like everything, until the next rage. Then, everybody shells out all over again just to get the latest window dressing.