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Um what? These restrictions are everywhere, just a little different across platforms. For example - All iTunes content is available on Mac, Windows & iOS devices, and all downloaded music is playable on all devices that support AAC. Apple doesn't offer a pure streaming service (AppleTV masquerades as one) so you're stuck with iOS, Windows, and Mac for purchased video content. - Google Play content can be streamed to…
You seem to be saying these restrictions are equivalent, but we're talking about video here, and iTunes is only available on Apple devices and Windows desktop (who wants to watch movies on a desktop computer anyways), whereas Amazon Instant is available on dozens of blu-ray players, smart TVs, set-top boxes, video game consoles that they do not control. Let's be clear here, iTunes is never coming to any non-Apple dev…
Amazon is in the content distribution business and playing catchup on having the devices to support it (because, for some reason, having their app on a smart TV and set top box doesn't seem to be enough).
This is a pretty good offering, but it's clear that, HuluPlus and Netflix aside, the big players [Google|Amazon|Apple] wants to have their own device ecosystem, and are fighting to differentiate theirs. For $99, these streaming devices are a disposable income purchase that gives you benefits in a particular ecosystem. Amazon has no particular advantage in this race yet, they're still coming from behind.