As screens get more and more detailed, trying to adjust pixels individually on say icons for each size the OS requires is pointless (I believe the count is 15 and rising). You need to design the icon with the usage in mind, and make sure it doesn't have too much detail which will matter when it is scaled. See the twitter icon for a good example of one which works at any size and could be scaled without losing its impact. IMO all icons on ios should be like that - simple and iconic. Same goes for icons in toolbars etc.

The vast majority of developers simply scale down icons and other assets to fit the various sizes Apple requires, so in practice the retina approach just means the same assets being scaled resized and cropped lots of times by developers to jump through the hoops Apple requires, and the problem is only going to get worse.

So I respectfully disagree, there are no easy solutions in this area, however I think resolution independence has better possible solutions than designing something as vector, then manually producing scaled rasters at every possible display size. At the very least Xcode should take care of that, but I'd prefer if iOS did, and accepted vector images within apps to start with - it could easily cache bitmap representations as it needs them, and then it could change those on the fly when screen sizes/resolutions change instead of requiring new binaries.

Sure, but Apple's code signing stuff could be modified to accept this if it doesn't already. You just need a way to express a requirement that file A or file B must be present, but you don't need both.