There are hundreds of devices out there capable of playing Amazon Video, they can't because Amazon either doesn't allow it (Android devices that aren't their branding) or charges a fee/device (ie. $1/Roku).
They want Vendor lock in, not in the sense that your data isn't portable, but that you rely on only their services. They do this by slowly pushing you onto more of their specific hardware and bundling more services essentially exclusively with their products
This is a valid point, and I suppose you could look at it as lock-in. Amazon of course would see customers simply choosing the better deal. Its what they do, after all.
Looking at it the other way, Amazon could build 20 teams to maintain the streaming software on all the devices, something that would be difficult to do at scale, profitably, while providing the solid customer experience Amazon has come to be known for. The detractors there would say "who cares if they don't lock you in, they cant, it sucks its slow and it crashes all the time." In my mind, Amazon is making the right choice, especially in the wake of Apple and Google.
Good thing as a customer I don't care. I can't imagine Roku would sell their device for $98 without Amazon, nor would a $69 device without Amazon Instant Video seem attractive.
As the customer, I couldn't care less. There is no "lock in" in this regard.
That's still much less locked in than Apple's approach (IIRC another manufacturer asked Apple to name their price, and was told they just weren't interested)
They want Vendor lock in, not in the sense that your data isn't portable, but that you rely on only their services. They do this by slowly pushing you onto more of their specific hardware and bundling more services essentially exclusively with their products