Starting May 1, the App Store will no longer accept new apps or app updates that access UDIDs. Please update your apps and servers to associate users with the Vendor or Advertising identifiers introduced in iOS 6
Starting May 1, new apps and app updates submitted to the App Store must be built for iOS devices with Retina display and iPhone apps must also support the 4-inch display on iPhone 5
Reportedly, this the new screen size requirements will also cause updates to apps or new apps to no longer support iOS 4.2 devices, because they'll have to be built against the iOS 6 SDK, which contains certain features that are incompatible with older versions of Apple’s software.
Since Apple is no longer allowing UDIDs, iOS 6 introduced the new Advertising Identifier system which essentially replaces UDIDs for developers. Apple is recommending that developers move over to this new system.