Not every place is bound to this. But some places are. PSN I think might be one of them. The game just isn't unlimited. PSN has to buy CD-Keys off the publishers and then sell those keys in the store. It just happens to all be behind the scenes. Again, not everywhere is bound to it, nor is the example I'm using 100% correct. PSN may not be one of the places that does it, I'm unsure how they do it now.
Movies on the other hand, no idea how exactly they work now-a-days.