Icons are, by definition, small. In its biggest form, on the retina display, users see a 144×144 pixel image. But developers are requested to provide a much bigger version: an incredibly super sized 1024×1024 pixel iTunesArtwork file. This much bigger and detailed version is used automatically in several places with different resolutions inside and outside the App Store, so, it is very useful providing a big file once and Apple has liberty to do whatever they need with your icon.
But, sadly, users don’t usually see this big, high-definition, awesome piece of imagery… Maybe you are a designer or simply enjoy icons, so:
Take a look at MaxiCalc iOS Icon in its full glory 🙂