Wonder if its a DRM issue, or other hardware security issue for Android devices.
I suspect it's to attempt to railroad people into buying the Fire range of Android-based devices. Not for me thanks! Why do I need another Android device?
Mind you, if the Lovefilm "By Post" application is anything to go by, Amazon can't find any decent Android developers in the world to employ because that piece of software is dreadful. Truly truly dreadful. Buggy, crashy, laggy, all three. They decided to not use native lists but use some weird HTML system; look at the licenses on that app. It's rubbish.
So, either railroading or they can't find decent developers to write a video streaming app. After all, BBC iPlayer uses Air I think. That was never a painfree experience on Android.