My question is around questions like this:
I completely agree that questions about networks outside of our control should be off-topic. In the linked question, OP is not referencing a specific network, if he had asked "How does AT&T reduce network speed?" - I would say it's totally off-topic.
He's obviously asking about QoS or similar technologies but doesn't have all of the context, I think anyone here can infer that. Part of learning is getting past the "known unknowns".
I think it's our responsibility in cases like this one to help them out a bit and encourage an edit to the question to make it on-topic, or like other questions reference him to another SE (QoS stuff would belong to us in this case).