Gaiman is right about Batman and Superman, but only if you go back more than 20 years ago. In the early 80s and prior, Clark Kent was the secret identity of a Superman who came complete with living knowledge of his Kryptonian heritage, while Batman was just a mask that Bruce Wayne wore to be more effective.

After about 1985, that flip-flopped entirely. Superman became the mask that homespun Clark Kent would wear so that he could perform great deeds without wrecking his home life, while Bruce Wayne effectively killed his own psyche in the course of becoming the Batman.

That Gaiman would be out of date (or just wrong) on his Americana really doesn't surprise me.