That doesn't surprise me. BSAC is a more structured form of group diving that included guided, continued practice. The notion that out of that you would get people that respond in line with their continued practice is exactly what one would expect.I run monthly open water training on the West Coast of Scotland. Students initially trained by other agencies, like PADI, are surprised by the their lack of OOG competence, including those holding Rescue Certification. This is only anecdotal though.
Students for all diver grades; Ocean Diver, Sports Diver, Dive Leader and Advanced Diver have to perform OOG skills and full blown rescues of an incapacitated diver. So yes, members do have to refresh their skills.
In many clubs the Diving Officer requires all active divers to refresh their rescue skills an the beginning of each diving season.
But that isn't representational of the bulk majority of divers and trying to extrapolate a survey of how that non-representational group to the larger majority is flawed. Now, you could argue that that structured approach is a better way to go overall, and that may be valid, but it also isn't realistic.