With the launch of iPhone5( 4 inch screen), most likely developers will be supporting both 3.5 inch and 4.0 inch screen for a while till most of the users have an 4 inch screen. When you create a project in XCode 4.5 and above, it creates the project with iPhone5 support. There are multiple ways to support both screen sizes e.g. create a separate XIB for each size, or use AutoLayout (iOS 6 and above) etc. This additional work adds to development and testing time. So if you don't have time and want to launch the app using the new XCode and want to drop the support of iPhone 5(4inch) you can do the following:

   * Remove the app from the device/simulator
   * Uncheck or delete the Default-568h@2x.png Target Dependency in the File Inspector tab
   * Clean & Rebuild the app and your app in iPhone 5 or iPhone Simulator will run in compatibility with letter boxing as show below:<!>

iPhone 5 Letterboxing

Later once you  are ready you can add full support for iPhone 5 with another release.