I think the point is any cryptographically secured POW system is that. But Bitcoin is a uniquely strong network in the space.
The POW produces nothing but a number. That number allows transfer of nominal units. Those units mean nothing without the proof of work TODAY when it is sent. Having a private key (secure or insecure) means nothing if you don't have the computational power to assure its passage to another address. What controls that computational power? The network of miners competing. THAT is power.
