Update: Apple launched iTunes Extras for the Apple TV on July 10, 2014.
Back on September 9, 2009, Apple introduced iTunes Extras, an HTML5-based way for studios to include digital versions of director's commentary tracks, behind the scenes videos, and the other kinds of bonus material commonly found on DVD and Blu-Ray. The original OS X 10.4 Tiger-based Apple TV was updated to support iTunes Extras, and it's musical cousin, iTunes LP. Then, on September 1, 2010, Apple announced an all-new, all-streaming, all-iOS second generation Apple TV, and... iTunes Extras didn't survive the transition. Not only that, they didn't get added back with subsequent software updates. On March 7, 2012, Apple announced the third generation, 1080p Apple TV, and still no iTunes Extras. Now, some 4 years later, iTunes Extras on Apple TV are still MIA.
Apple still sells movies with iTunes Extras, but those extras can't be played on the Apple TV, or on the iPad, iPod touch or iPad - the most popular and common places they'd likely be played. They can only be played via iTunes on Mac or Windows.
I love bonus content - making of, creative process, deleted scenes, bloopers, and all the rest - as much as the TV shows and movies themselves. It's why Hollywood succeeded, on numerous occasions, in scamming me into buying the same movie more than once - the initial release, and then the bonus-laden special edition that followed. The idea of all that content in digital download form is incredibly enticing. Not being able to access and enjoy it on the best possible devices, including the Apple TV, is beyond frustrating.
Right now I'm downloading more than 5GB of bonus content from Star Trek: Into Darkness to iTunes on my Mac, and as soon as it finishes I'll be AirPlaying it to my Apple TV. It's not ideal by any means, given the amount of time it takes to download (rather than just stream) all that content, but it's all that's currently possible.
Despite its money, despite its size, Apple is still resource constrained. I understand that. They can't do all things, all the time. But it's been 4 years since the feature was announced, and 3 years since it was lost to the Apple TV. That's a lot of time, and a lot of downloading, and lot of poor customer experience.
Let's get iTunes Extras on the Apple TV already.
(For even more Hollywood insanity, check out The Digital Bits' story on how Star Trek: Into Darkness bonus features are being used as marketing ploys at the expense of customers. Maddening.)