<p>Well this is Action Comics Vol 2? I've not read. In the Pre-Crisis and Post-Crisis the explanations to this vulnerability were: 1) In Krypton, as a science-oriented planet, magic was very rare, then kryptonians have no defense against it because had no exposure (the same principle of bacteries, for example). In Earth, various of our ancestors had relationship with the Homo Magi, then teorically anyone with enough occult training can perform rituals (but not directly cast spells, as do true Homo Magi). 2) Superman's biomatrix is his most powerful asset, but the strength of this field is also its greatest weakness. Its permeability to certain wavelengths makes him vulnerable to certain radiations, particularly magical energies whose chaotic electromagnetic or extra dimensional signatures disrupt this force field. Superman's vulnerability to magic varies depending upon the special effects of the magic. No magic seems to be able to directly destroy him unless it comes from a semi-divine or divine source. He can be injured and worn down by magical entities. Magic can have powerful and unpredictable effects on Superman and his magical enemies have often proven to be the most dangerous. </p>