They don't, but the argument here is about Sideshow's bad business decisions, isn't it? That's why I stated that as long as they do NRD refunds, I think it's hard to complain. That was my point, and nothing else.
However, as an aside, They actually don't have the right to say no in a technical sense. Legally, they don't have a leg to stand on, and a credit card company will always side with the customer. No one ever has to let them keep their NRD. They could cancel your account out of spite for doing it, but you could always get it back. I'm sure they know this, and thus why I've never had an issue. It's like businesses that try to tell you you have to spend a certain amount in order to use a credit card. It's just not allowed.