Apple states that their license for the YouTube app has expired and it will not be included in iOS 6. Google will be providing one in the App Store. The move seems to be part of a more general eviction of Google services from Apple products.
With the release today of iOS 6 beta 4, Apple removed the YouTube app from the operating system. The YouTube app has been on the iPhone from the first version, and in fact has been a mandatory component which users could not even delete. It appears now to be a victim of generally hostile relations between the companies, especially on Apple's part.
"Our license to include the YouTube app in iOS has ended," Apple said in a statement on Monday. "Customers can use YouTube in the safari browser and Google is working on a new YouTube app to be on the app store."
Early in the life of iPhone Apple needed Google's help to get YouTube supported because the lack of Flash support on the device. Support for iOS may have accelerated YouTube's move to H.264-encoded video. YouTube has since changed codecs due to licensing issues.