Of course there's limited commercial value in holding intellectual property without legal protection, because there's limited commercial value in holding any type of property without legal protection. But that's completely beside the point of the natural law argument.
For what it's worth, I don't actually agree with this argument; I was just pointing out that it's possible to use natural law to argue in favor of intellectual property rights.
One can only expect to command a copyright-level price for a copy if other people obey a copyright-like law to not make other copies.
But that is just going in circles. One cannot justify something based on itself.