There's actually quite a few systems which do exactly that. Funnily enough, all use DRM.
Why, precisely, do you think you can't play the video file in a player of your choice? That is literally what DRM is - technical restrictions against using content you have purchased in a manner you desire. They provide the file in an encrypted format that only their own player can decrypt.
When iTunes used DRM for music, only Apple's devices could play music you bought from iTunes, too.
However you're right - the iTunes purchasing example shouldn't have been part of my previous response. On the other hand I think DRM is fine, if not a necessity, for a subscription service like Netflix. It is basically renting content and my expectations towards these services are very different from a store that offers purchasing, which should absolutely be a DRM-free experience. The fact that it's not is exactly the reason why I don't buy films on those platforms, unlike music, which is available countless large and niche stores.
This is not comparable in my opinion. Music was bought, downloaded, stored locally and used on countless devices - from your living room setup, your NAS and media center, to portable players or your car. It made no sense to restrict that kind of content to specific software like iTunes.
A Netflix stream doesnt face the same problems. Compatibility isn't an issue here. Most consumers will never run into problems with Netflix' DRM.
That said, of course if it was possible to buy and download movies for permanent offline viewing, similar to music purchases, it would be absolutely necessary to provide that content DRM-free.