Maybe the Amazon Video via AirPlay is not “HD”. But I’ve been watching Amazon Video via Airplay after downloading and Netflix video streaming nightly for the last week or so. The quality of the Amazon Video via AirPlay of downloaded content consistently beats Netflix streaming hands down.
I completely disagree, Netflix streaming (at least on my ATV3) does stream in HD and 5.1 audio, Amazon video via AirPlay does not have as high a quality, it is obvious to the naked eye. But, I did have issues with Netflix back when I had a low bandwidth DSL connection, so, I can see this, but, if you can get 5-10GB d/l speeds, depending on how many ppl use it, you should get much better results w/Netflix.
...AFAIK none of the ATV4 video apps (e.g Netflix, Hulu, etc.) allow you to download content for viewing later. Is that just a coincidence or could that be because Apple doesn’t allow it? And if the later, is that part of why Amazon hasn't developed an ATV4 app?...
This has nothing to do with Apple, it is the way they do things everywhere, not just on Apple TV. I don't believe you can download content for later viewing with iTunes on your ATV4 either (but I do not own one yet), only on your iOS devices or with iTunes and your computer.
In fact, I have a big beef about watching online/streaming content with ads...except for Netflix, iTunes and Amazon, (and a few pay-too-much-per-month apps), they (virtually all the content providers) have subtly made it so that you cannot skip or fast forward past ads, no matter if you watch on computer, or set-top box, anytime you watch a TV show over the internet, you are forced to go through the ads. This is something that everyone needs to be aware of...and I have given Apple feedback that if they come up with channel packages we absolutely need either: no ads, or a way to skip or fast forward through ads...if you can do it with the cable boxes, you should be able to when you pay for it any other way. When it's free, I guess I have to put up with it.