The next update of my iPhone app will be targeted for iOS7 only. A couple of questions?
Does this mean I can delete all the non-retina images from my app?
If I have only retina images left do I still need to mark them @2x?
Does Apple keep older iOS versions of my app on the store so those running older versions of iOS who have bought or want to buy can still access it?
Any help would be most appreciated.
Yes you still need to have the @2x at the end. Yes you can drop all the non-retina images but could affect performance as even the newer devices will use some none-retina images but the main performance hit was to iPhone 3GS and below but as iOS 7 will not run on iPhone 3GS or below it isn't a requirement you'll just have to handle the performance issues. No Apple do not keep hold of older versions of your app on the app store, if you drop support for it then it is gone.
To answer the second part of your question YES, Apple does indeed store older versions for download.
For my app Parkable I created one for iOS5/6 then when 7 came about I specifically targeted it and dropped support for older iOS builds, now if you're not on 7+ you can still download the old version (instead of the old error telling the user to update their OS). This happens automatically as I recall, simply change your deployment target in both your project and target under the info tab.
Feel free to test if you have a pre-7 device (iPhone or iPad) and 7+ device https://itunes.apple.com/us/app/parkable/id577954935?mt=8&uo=4
来源：https://stackoverflow.com/questions/21164232/can-i-dump-my-non-retina-images-for-a-ios7-only-app