On those devices, Apple simplified the way UI layout is done by fixing the usable coordinate system at 320x480. As an app developer, you position things on ret

On those devices, Apple simplified the way UI layout is done by fixing the usable coordinate system at 320x480. As an app developer, you position things on retina devices no differently than on non-retina devices; placing a button at (160, 240) puts it at the center of the screen in both cases. The higher resolution / DPI is only used by the low-level font and graphics toolkit. As far as the developer and user are concerned, the device has a 320x480 "desktop" either way. You can imagine an alternative scenario to this in which everything on the screen is half as big as it used to be yet equally detailed, with four times as many icons fitting on the home screen as before. This is what it would be like if the full resolution of the retina display were utilized just to provide more real estate instead of more detail.