Re: Great but
This is pretty normal, and it's all about funding. It actually costs quite a lot of money to develop, maintain and improve standards, way more than the amount of money it costs to be a member of the SIG. Being a member gives you access to some very valuable intellectual property. It probably also involves you giving a commitment to not rip off the IPR (i.e. pay any royalties on relevant FRAND patents that are involved).
For software, even if there was a professional crew writing it or developing a standard for it, there's precious little more than manpower involved. Whereas hardware standards like PCIe, someone may well have spent several hundred million dollars on silicon design and fabrication, just to see if it actually works. So it's understandable if the body(ies) that developed it are a little bit reticent to just give all that away for completely free; FRAND royalties really count as a motivation to do the initial expensive work.
Besides, someone has got to manage the list of vendor and device IDs.