Well, OS X was in fact designed to match the hardware. The original Aqua UI was more or less an extension of the blobby plastic Macs of the time -- the turquoise G4, the first iMac, the 'clamshell' laptop etc. The colors, the translucency, the pinstripes, it was all reflected in the UI. Then of course the hardware changed radically, while Aqua has been phased out gradually... though it lingers in spirit.
Aqua was refreshing at the time. The iPhone brought similar refreshment to a world of ugly UIs on mobile devices. But lately the pendulum has been swinging away from that style. It's been-there-done-that, no more childish glee over bevels, gloss and drop shadows. Every time that UI or website graphics get revamped these days, it's towards a cleaner and more streamlined design that looks more like print. Using the Pepsi logo as an analogy, Windows 8 corresponds to 'current design' while OS X/iOS is on 2003...
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