It is. You can either be purchasing a license to a movie, or purchasing the movie itself. You have never been purchasing the movie itself from these services, because you're not entitled to it even after you purchase (i.e. there is DRM, etc. preventing you from ever getting it, you don't get it in any alternative forms, etc). If you want to own something, you buy on iTunes, where they let you download DRM-free copies, to do whatever you want with. But if you buy it on PlayStation, Amazon, etc. you are only getting a revocable license. You are only buying a revocable license. That is what "purchase" or "buy" means, because you're "purchasing" or "buying" the license, not the movie