They are non-changeable buttons, and if you don't sign up they take you to a page where Roku earns a commission if you sign up. Why won't Roku let me change what the buttons do... oh, it's because they were paid to put those services there. Your excuse that they are the most popular services is false because they aren't consistent across devices. They sold ad space on their remote. There isn't a spin for that that fact.
The screen saver and menu ads don't just show ads for additional content but don't let that fool you. Ads for movies and videos are still ads. It shows content for subscriptions you don't have not ones you do. And again, Roku earns commission if you sign up. They are ads that take up 1/3rd of the screen.
There are no straws to grasp. As long as Apple keeps the UI looking nice and responding quickly it is far superior than the economy stick roku is pitching. Seriously, they admit to it. Read up.
Look dude, if you want to use the limited Apple service and live in their walled garden, no one is stopping you. But your attempt to show everything Apple does is "good" and all others are "bad" is only going to limit your options. Roku offers a "we have no dog in this fight" great line of services. I use the Netflix and Amazon buttons all the time. People who don't have the services press on them and are given an easy way to sign up if they want.
And so what if Roku earns a commission, so does Apple on all their services to include the app store. The new Apple TV App will be included on the Roku device along with Netflix and others. Oh but that will be okay with you right? People should have Apple on their devices... It is only bad when it is someone else.