Did their old service agreement say squat about queues in some asterisked fine print about "Unlimited"? One might have the impression that they could copy up whatever they needed.
They don't make copies, that would be illegal and the publishing companies hate rental companies enuogh as it is.
I think there might have been something pointing out that there were logistical limits, which there are. Because you pay by how many you can have out at a time there's a limit on how many movies you can get in any defined period. Recently they added the throttling to the terms of use. I think when I originally joined they weren't doing that because they didn't have enough subscribers for it to be an issue, even if they did decide to put you at the back of the line you'd still get your movie mailed out that day because the line was short. In the interim they've added a couple million subscribers and the line has gotten longer and the throttling is visible.