App Store Screenshots go Retina Only
09 February 2012
Via an iTunes Connect email: > Required iPhone & iPod touch Screenshot Upgrade for Retina Display > > When you create or update your apps in iTunes Connect, you must upload screenshots that are high-resolution. We require your screenshots as high-resolution images so that your app is optimized for the Retina display. When browsing the App Store using a Retina device, low resolution images stand out like a sore thumb.
See also, images on most websites.