Commercial success depends on a solid technical infrastructure. Netflix evaluated Bittorrent vs centralized distribution and went centralized. YouTube did the same. This indicates that BT is not technically better than a centralized model.
But I think the only reason Netflix doesn't use BT is that the content owners are super-skittish about people having a copy of the data on their computers instead of streaming it and throwing it away. So even if BT is a better technical solution, it's politically unworkable.
I would disagree with this point
>This indicates that BT is not technically better than a centralized model.
It indicates that BT didn't provide something that Netflix et al did require. I imagine that is something like maintaining control of all digital copies of a work as you went on to suggest. This is not a technical limitation but rather a business need. So BT may be technically better (I imagine in terms of resources required to provide content it is superior) however it didn't meet the business case as well as a centralised solution did hence BT doesn't get used.
But I think the only reason Netflix doesn't use BT is that the content owners are super-skittish about people having a copy of the data on their computers instead of streaming it and throwing it away. So even if BT is a better technical solution, it's politically unworkable.