Yes that's who I picked but it does not need to be them. My reading of it and looking at the other listed clubs it could be any club who has an interest, within reason.
I must say I have know knowledge of the NDSOC I just did a quick Dr G. I was actually looking to see if the Nissan Datsun Drivers Club still existed in NSW and it does. I just picked NDSOC as an example as they seemed boarder based not just Rally/CAMS.
I am betting that what you say is very true for a lot of special interest clubs.