If I had to guess, licensing. I imagine studios see AirPlay (legitimately or not) as a DRM backdoor by letting the stream out of the app; and thus don't allow it. Note HBO Go and Netflix apps don't allow it either.

I believe HBO's reason is that they're not using MPMoviePlayerController (the default video player). It looks like the native one, but I remember seeing jaggies around the icons after upgrading to the iPad Retina.

If I had to guess, it would be that they have some sort of proprietary DRM going on and have their own player for it.

Netflix allows it (in the UK, at least). I use it every so often when my Apple TV borks.

You're quite possibly right though. The 4oD app (British TV channel's streaming service) also blocks Airplay for licensing reasons.

Netflix does allow AirPlay in the US.

In the past I've worked on a number of mobile projects for very large organizations (e.g., major sports organizations) that have restricted certain video streams based on the screen size of the device.

In most of these cases, it was due to contracts that were made 5-10+ years ago that gave some company the exclusive rights to their video on various size screens (e.g., 'screens less than 5" diagonally'), or even TV/'Not TV'. Sometimes it was even split up between companies across 3 or 4 different ranges of screen sizes.

In some cases, we had to build the apps to use Company A video streams on iPhones, and Company B streams on iPads. To make things worse (at least for the consumer), sometimes the app was allowed to AirPlay from the iPad but not from the iPhone, or even not at all, because of these contracts.

Macworld recently wrote about this: http://www.macworld.com/article/1168038/playing_amazon_insta...

As others have commented, it's a licensing issue.

One workaround is loading the Amazon Video Player in Safari on a Mac, then mirroring the display on AppleTV. Looks best in full screen mode.