I couldn't say about the magazine, but it's not at all unlikely that there is some sort of sponsorship. I feel the the GS paints are very similar to the
Tamiya paints, they even smell very much alike, color by color. I would say that GS paints of a very high quality (as are the
Tamiya paints). As with a lot of other stuff in our hobby, I it's often up to; personal preference, geographical availability and palette, to decide whether one brand is more common than others, in certain places or contexts.
Moving chemicals across national borders is still a very challenging endeavor, and often a major contributor to one brand being able to penetrate a certain market with greater ease than others.
/Daniel