This is pure speculation and hopefully I’ll hear back from the engineers after they come back from the long weekend/holiday, but if I were to guess, I would think this would be in order:
“Icon.png” , 57x57
“Icon@2x.png” , 120x120
“Icon-72.png” , 72x72
“Icon-76.png” , 76x76
“Icon-76@2x.png”, 152x152
I honestly don’t think Apple really looks at the file name for anything meaningful. iOS2 did, but with iOS 3 you provided the file name of the 57x57 using the CFBundleIconFile key. iOS4 added the array of keys: CFBundleIconFiles = {. I suspect that Apple reads the files you specify and actually opens up the file to determine it’s size and hunts for the icons it’s looking for. If that’s the case, it probably wouldn’t hurt to provide more icons than they will actually use and maybe we should do:
“Icon.png” , 57x57
“Icon@2x.png” , 114x114
"Icon-120.png, 120x120
“Icon-72.png” , 72x72
“Icon-72@2x.png”, 144x144
“Icon-76.png” , 76x76
“Icon-76@2x.png”, 152x152
I don’t have any apps that are nearing submission so I don’t have a real good way of testing this right now. Again DISCLAIMER I’m guessing here, lets wait on the engineers.
(And don’t forget to include the four spotlight icons: 29x29, 58x58, 50x50, 100x100) Of course Apple makes then optional.