Here are some numbers to blow your mind: The original Macintosh, released in 1984, had a monochrome 512×342 pixel display. That was 175,104 points. Today, the icons on iOS are 512x512 pixels, drawn from a 16.7 million colour palette plus 256 levels of transparency.
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Twenty-eight years ago, a monochrome icon on the Mac was 16x16 pixels. It only took 32 bits of memory. Compare to the 512x512 pixels of each iOS' icon. It takes four times the total video memory of the original Mac to represent a single icon in iOS at full size. Of course, iOS icons are not shown on screen at that size. They are much smaller. Eventually, however, you can be sure that there will be displays that would require that insane pixel density.
What is remarkable is that the absolute size of the icons remains more or less the same. It's an amazing increase in the density of information required to represent the exact same object with the exact same meaning. Eye candy is expensive.
Another comparison: the new iPad 2012 has a 2048x1536 screen, with 9.7-inch physical size. That's four times as many pixels long by 4.5 times as many pixels tall as the original Macintosh, which had a 9-inch screen.
If anyone had told me this when I tried my first Mac, back in the '80s, I would have never believed it.