I bought a hard cover for office. Agree about ending in book and felt Allan Moore wrote himself in corner when I first read it 1987. Moore has been wrong before which he rarely admits.
Regarding using made up characters rather than Charlton characters:
Moore had initially believed that original characters would not provide emotional resonance for the readers, but later changed his mind. He said, "Eventually, I realized that if I wrote the substitute characters well enough, so that they seemed familiar in certain ways, certain aspects of them brought back a kind of generic super-hero resonance or familiarity to the reader, then it might work."
It worked extremely well.