Apple stated today that gone from iOS 6 (to be released sometime in the next several weeks) will be the YouTube app. According to Trudy Muller, spokesperson for Apple, Inc., the company's license to include the YouTube app on it's mobile devices has expired, but further information on the subject wasn't mentioned.
I can only surmise that given Apple's strong anti-Google stance, they're not exactly heartbroken about the license expiration. It's been common knowledge for some time within the Apple community that the company is desperate to break its dependence on Google with some core aspects of iOS - namely the engine that powers its Maps app. iOS 6 promises to break that chief dependence by introducing Apple's own iteration of navigation.