This does not mean that there is any binding between the namespace that the resolution protocol. However, the reality that clients can and will do whatever they want is also recognized. Client developers are hereby warned that implementations that make assumptions about the namespace of a naming authority are considered non-portable at best and outright dangerous in normal environments. Within a URN, the name space is identified by a scheme. I think this sentence was a hold over from an earlier version.
Life is a game.
Someone wins and someone loses. Get used to it.