I suppose a true germophobe would be repelled just by the thought the reading material being exposed to fecal gasses which contain minute microscopic particles, which give methane its smell.
But then, there's a more logical reasoning. Who knows what really goes on in there behind closed doors? Does the person reading the magazine 'scratch' while they read, as you suggest? Or perhaps they wipe, quite possibly soiling their fingers, and then pick up the magazine with unwashed hands....maybe even leaving a stain on it? Maybe they insert a suppository, and then continue to turn the pages. Ugh.