That letterpress app icon is exactly what Apple are being reported to move away from, its fake analog and has become very outdated.
Flat design takes away all the unnecessary effects and gloss and isn't made to look like analog, like a lot of the fake calendars/clocks Apple does.
Here's an example from Google of flat design, there are no drop shadows or unnecessary effects, its all made in block colours:
[url=http://i62.photobucket.com/albums/h93/joe8979/ScreenShot2013-05-05at124309_zpsc9b8d815.png]Image[/URL]
[url=http://i62.photobucket.com/albums/h93/joe8979/ScreenShot2013-05-05at124520_zpsc005596c.png]Image[/URL]
Flat will become boring and outdated in less than 2 years. Apple switching to flat now, will only prove they are chasing history, instead of making it.
Of these two app examples which do you prefer? To me the first one looks more dated almost like a house that has brassy hardware everywhere. Some would argue the first is better because it makes the buttons look clickable/tapable. But I don't think it's hard to figure out what to tap in the second example.
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Flat will become boring and outdated in less than 2 years. Apple switching to flat now, will only prove they are chasing history, instead of making it.
But if they don't update the UI (whether using flat elements or not), then they will become farther behind. The style they use for backgrounds/gradients/icons is unimportant to the overall user interface improvements that are needed.
70% of those people probably dont even know what "flat" means and simply bitch because all they "heard" is that windows 8 is apparently "flat" and they hate it