Apple today released iTunes 11.3 that adds iTunes Extras for HD Movies in addition to SD variants.
Here are the release notes:
iTunes 11.3 includes all-new iTunes Extras for HD movies. iTunes Extras can include behind-the-scenes videos, short films, high-resolution image galleries, director’s commentary, scenes, and more. These immersive iTunes Extras can also be enjoyed on Apple TV with Apple TV Software Update 6.2 now, and will be available on iOS 8 this fall.
New iTunes Extras will be automatically added to your previously purchased movies as they become available—at no additional charge.