Using ADT I can set compilation platform -platformsdk to iOS5 for retina display. Does it mean app will work only with iOS5 and does not with iOS4? Can app automatically reduce resolution to iOS4 and I still can see minimum iOS requirement is 4.0 or I need two application for different iOS?
For using the retina display capabilities of the new iPad, you need to set the platform sdk to iOS 5.1. It does NOT mean that your app will work only for iOS5 ( and not iOS 4). Also, You dont need to submit two different applications for ddifferent iOS. Your minimum iOS requirement will remain set to 4.0 as before.