>So you just use a larger low dpi icon. The problem is that the icon at the same physical size now has much more details and looks less clear.
In what way does it look "less clear"?
The problem with showing more details on the low-dpi screen for a 16x16 icon was the low resolution of the screen.
A hi-dpi screen doesn't have this issue. It's effectively showing 32x32 quality on the 16x16 "virtual pixel" size.
At worse, it would have looked as good as a 32x32 icon in a low-dpi screen. But in the hi-dpi it looks even better, much sharper and refined. You're getting an icon that's as good as a 32x32 icon would be on a low-dpi screen, but with half the physical size, so that it appears twice-as-detailed as a 16x16 icon would be.
The top comment in this thread details why it looks clear: some icons have different proportions for different icon sizes to make sure things look okay. So the problem is that proportions planned for one physical size are used for a smaller physical size.
16x16 and 32x32 allow for the same proportions though (including alpha-ed out pixels).
And if the icon looks ok in 32x32 on a low-dpi screen, it will look doubly so as a 16x16 virtual pixels with doubled resolution underneath in a high-dpi one.
Not necessarily. When the first iPhone came out with retina display I eventually realized that the contacts app had incredibly tiny letters on the tabs. It was only visible if you looked very closely but was an amazing touch of polish.
In what way does it look "less clear"?
The problem with showing more details on the low-dpi screen for a 16x16 icon was the low resolution of the screen.
A hi-dpi screen doesn't have this issue. It's effectively showing 32x32 quality on the 16x16 "virtual pixel" size.
At worse, it would have looked as good as a 32x32 icon in a low-dpi screen. But in the hi-dpi it looks even better, much sharper and refined. You're getting an icon that's as good as a 32x32 icon would be on a low-dpi screen, but with half the physical size, so that it appears twice-as-detailed as a 16x16 icon would be.