I won't ever buy Amazon Prime until they have a video app on the Apple TV. If I can't use what I'm paying for, then screw Amazon, I have the patience to wait for normal shipping times.
I think Amazon is probably ok with that. They currently have a pretty good base of customers, and they are trying to build more loyal customers (like Apple has), rather than build something that works alongside Apple products. They don't want to cooperate with iTunes in your home... they want to replace it.
There will still be some folks (like myself) who will fork over the $99 for shipping, and get the added benefit of being able to stream some media (even if I only use it a few times a year). But those aren't really the customers Amazon is after... which is why they aren't on the Apple TV.
They want the kinds of customers Apple has. The kind that use their services, but also pay for their hardware, and purchase lots of movies, music, and apps. That's what Amazon is trying to build... so discouraging folks from buying an Apple TV and avoiding competing with iTunes in those homes kind of makes sense.
I'm just not going to upgrade to the Apple TV 4 until they can get channels I use like Amazon and Vudu and Slingtv..... Blame whomever you want but those channels are found on LOTS of other devices, so they are not restricting their apps to only their own device like Apple does with itunes. I'm not going to let anybody tell me what channels I can and can't use. My Apple TV 3 collects dust because the channels I use are mostly on my Roku.
Like my above post... I think Apple is probably fine with this. Amazon (as well as Vudu) are in direct competition with iTunes... which is not something that is true between Amazon and Roku. Amazon doesn't want to be in the Apple TV for all the reasons I've already stated. If that service is important to you... enjoy your Roku. It's a fine option.
As for Sling, they've stated that they are working on an app... but I'm wondering if they've seen the writing on the wall with Apple's attempt at streaming service.
Sling is owned by Dish, so they are probably waiting to see if Apple is going to be purchasing any/all of TWC - which would be another direct competitor. You would never see Dish cooperate with any TWC services... so this is probably no different. Just like Amazon, they want to discourage folks from sending money to a direct competitor.
In my opinion, Apple's streaming service is not an if, but a when... and at that point, they will also be in direct competition with Sling, regardless of this TWC business.
All of that to say, Apple customers are kind of experiencing the pros and the cons of owning products of a company that is in direct competition with such a far reaching group of companies. We are currently in the growing pains of some of these services (think Apple Maps)... but it should be working nicely soon enough.
For my part, I have Hulu, Netflix, a decent size personal iTunes library, and an antenna with the Channels app (not to mention a sideloaded Kodi app), so I have more than enough content to keep me happy until some of these other services reach completion.