Apple looks for certain Icon files without specifying them. This is a legacy IOS 3 thing. I think it will find Icon.png by itself. However if you want to include the retina iPhone and the iPad sized icons, or if you want to include the various spotlight Icons, or use different names for them, you have to include them in your build.settings.
This is the full set that Apple will use:
CFBundleIconFile = "Icon.png", CFBundleIconFiles = { "Icon.png" , "Icon@2x.png" , "Icon-72.png" , "Icon-Small-50.png", "Icon-Small-50@2x.png", "Icon-Small.png" , "Icon-Small@2x.png" },