iPhone

Apple quietly posted this announcement requiring all iOS developers to "Build Your Apps With Xcode 5.1.1". Apple enforces this when you try to upload your binary to the iTunes App Store:

ERROR ITMS-9000: "This bundle is invalid. New apps and app updates submitted to the App Store must be built with public (GM) versions of XCode 5.1.1 or higher and iOS 7 SDK. Do not submit apps built with beta software.”
Today, we've addressed this in the last public release (2189). Just rebuild and submit. You can also use daily builds 2306 or later....

Starting in daily build 2014.2277, we are changing the minimum supported version on iOS from 5.1 to 6. This means that if you do a device build with 2014.2277 (or later), your app will not run on a device whose version is below iOS 6. This change is needed to move our iOS architecture forward, and finally pay off technical debt that has been accumulating for nearly 18 months, which is an eternity in the mobile space....