I added Default.png and the other variations for iPhone 5, retina display fils and they appeared in the Resources folder. These are for loading screens and are built in as part of the bundle after you add them.
However in doing some work on rolling my own Splash screen so it can have text added, I decided to remove them.
In Xamarin Studio (on Mac) you can unset them, but compiling gave 2 errors about missing files. Looking in the info.plist on the source tab revealed that two strings were still there so I manually removed those. I did a clean then a Build and still got the errors. I did a clean and a Rebuild and still got the same errors. Finally I closed Xamarin Studio down, then reopened it and it built fine. Just a minor irritation.