Good point. Though that puts this somewhere in a middle ground between a best effort stream and a reliable stream. The ability to throw away data you don't care

Good point. Though that puts this somewhere in a middle ground between a best effort stream and a reliable stream. The ability to throw away data you don't care about is not absolute but is instead conditional upon successfully receiving more data. In a true best effort streaming system, the sender wouldn't retransmit. With this scheme, the sender might retransmit, sometimes, depending on whether certain packets get through and allow certain acks to get sent.