The main problem here is that PSN accounts weren't for the benefit of the customers. Sony decides to cut loose Arrowhead tomorrow and keep the IP, the game would continue to operate as usual. Yes, they probably would have to get marketing departments, and the services that Sony was providing as publisher, but those are easier to scale up/get a partner to manage them.

The PSN requirement wasn't baked in the game, it was tacked on 6 months before release. That's why people say that while it was "required" is not "needed". Required should be kept for things that without them, the system would not work.