The point about censorship is an important one. If the system is build focused on a central hub this can be prevented directly in the smart contract. If the system is more general and everyone could potentially be a central hub (note that any store could what to have a node to receive payments, or small communities would also be interested in having small central hubs, etc) then it would be difficult to control censorship.
All the other points described by jtremback are a bit forced. In particular I do not understand the payment processor part, the central hub do not receive funds from anyone, these will be in the smart contract of the main system.People are just storing funds in a contract, those funds are realesed when the users show a signed agreement between them, is there something I am missing?
I think you guys are misunderstanding my post. I am comparing a payment channel system with a single hub (for example Perun-style) to a centralized payment processor like PayPal. My point is that the benefits are minimal.
Hacking the hub will basically imply that the privatekey of the hub is compromised, this put on risk only the funds of the hub. I think the main point from @adamskrodzki is that attackers will aim at the hub as it is the one with a considerable amount of money.