This is the viewpoints I have as well. Deagostini are pretty well established. As
@Joe Mac said, they aren't just releasing records with magazines but also diecast models, etc usually with a large scale franchise attachment such as Star Wars and Lord Of The Rings. I fully imagine they have the licensing for the stuff they put out, it would be far too easy for one of these large scale companies to just sue them to oblivion.
These Jazz At 33rd releases were definitely part of a magazine series, as you both said. They mention the magazine on the stickers and insert that comes with them. Zavvi definitely just bulk bought a ton of them to resell as bundles. Really great value as well, I seem to remember each coming out to only a few quid per record. Lots of us here bought them at the time and swapped around.