Apple has notified developers of iOS Developer program to only upload images for Retina Display for their iPhone and iPod touch apps while submitting them to the App Store.
Prior to this, developers could upload images for Retina Display, but it was not a mandatory requirement.
Apple has issued the following notification:
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.
The requirements for high-resolution images are 960 x 640, 960 x 600, 640 x 960, or 640 x 920 pixels. Images must be at least 72 dpi, in the RGB color space, and the file must be .jpeg, .jpg, .tif, .tiff, or .png. You can update your screenshot files at any time in iTunes Connect.
Developers need to meet this new requirement even when they submit an update for their existing apps. While this could well be a house-keeping exercise to ensure that the images in the App Store look good on iOS devices like iPhone 4 and iPhone 4S with Retina display, it has also led to speculation that iPhone 3GS may not be around much longer.
We don’t agree. While we expect Apple to phase out iPhone 3GS when it launches the next generation iPhone, we don’t think Apple will stop supporting iPhone 3GS so soon. Also screenshots are used in the App Store and has no bearing on the support for a particular device.