I don't understand why they don't do this automatically. For any image where you provide both retina and non-retina, strip out the one that isn't needed when sending it to a device.
Wouldn't this make signing more complex? Currently the bundle doesn't change after you sign it on submission, but it would have to if resources were getting stripped.
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.