The Mac user interface, with its menus, radio buttons, checkboxes, windows, title bars, and yes, scroll bars, is built on an entirely different interactivity model than iOS. The Mac UI was built for a pixel-accurate indirect pointing device; iOS was built for direct manipulation with one or more fingers. The visual similarity of on-screen elements and the technical feasibility of porting them from one OS to the other should not blind us to these essential differences.
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John Siracusa, perfectly summing up the Big Philosophical Problem I have with porting iOS touchy-feely interaction to the desktop OS.
Mac OS X 10.7 Lion: the Ars Technica review