I'm not getting through, am I?
Apple "sell" iTunes movies on the basis that they can be catalogued on - and streamed to - an Apple TV. They also provide short term rental on the same basis.
In arbitrarily removing movies for streaming, buying a movie amounts to no more than long term rental, which is disingenous. If they changed the "Buy" button to "Long Term Rent" I would not be so annoyed.
There are any number of ways of downloading, movies, storing them, making backups, making backups of backups, plugging extra things in and - if you're lucky enough to have the right equipment at the time - viewing them.
Guess what? When Apple invite me to buy a movie on my Apple TV, I expect to be able to play it. End of story. Without any of the above nonsense.