User interface design -- fad or function?

Microsoft started with the flat Metro interface of Windows 8. Apple flattened iOS 7 and now Google has flattened their logo.

Is this based on human-computer interface research or is it style and fad? Years ago, I taught an HCI course in which we read about controlled studies in making user interface design choices. Google is said to be engineering driven, researching everything from the optimal number of seats at cafeteria tables to the number of pixels devoted to a particular icon on the screen.

But, I have the feeling that the rush to simple, flat user interfaces is driven by fad as much as function. My wife uses an iPhone and an iPad. She is probably a typical non-geek user -- using relatively few apps and features. Our daughter was all excited when iOS 7 came out -- she grabbed my wife's iPad and iPhone and installed it the next day.

After using iOS 7 for a few days my wife says she sees no advantage for her usage mix -- the only change is that she has to learn how to do what she always did in slightly different ways. She also likes 3-D buttons that are obviously clickable and give feedback when you click on them.

My wife thinks it is fad, not function and it reminds me of the Pantone's annual fashion color palette and their color of the year:


If these changes were driven by functional considerations, I'd love to see the old-fashioned HCI research that led to them. If not, fads tend to be cyclical, so we can look forward to a return to 3-D skeuomorphism in a few years. As you see below, the designers are already working on them.


(You can make your own goofy logos at http://createfunnylogo.com/).

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Update 9/29/2013

This child was even more upset than my wife with iOS 7: