According to this thread on the iPhone Dev SDK forum, when the icon has been downloaded in .png or .tiff format, iTunes will automatically add shine. However, when loading as .jpg gloss was added.
I reloaded the Store Store icon as 512 x 512 @ 72 dpi (Jpeg). Initially 512 x 512 @ 300 dpi (tiff). Hope this helps others.
This seems to be a strange problem - another user reports that this is a bug with iTunes Connect, as a result of which it does not comply with UIPrerenderedIcon .
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