I think I understand this part of the inflationary phenomenon. The .303's appeal to a wider audience, notably the shooter-collector. They want a nice piece of Canadian history that represents the issued service rifle. While rarer, I believe the CNo7 appeals mainly to the collector because of it's .22LR chambering.
The shooter-collector community in Canada(note I place shooter first, as that's what they most want to do with the rifle) has grown significantly recently due to the Internet and sites like this and CGN, IMO. While this does drive prices up, I feel it bodes well for the future health and continuation of our hobby.