At Sean Collins' blog he responded to Curt Purcell's remarks at length, bringing about a good response from Curt in the Comments section. But I want to direct my remarks to one niggling point of Sean's that Curt didn't address.
I agree with Sean that there are cultural limits on how far most superhero comics will allow themselves to get from the ideal of "costumed hero appears in a reality just like ours." I don't think it's entirely a function of the way the companies of Marvel and DC want to keep their universes a certain way, for during the flowering of the 1980s alternatives most superhero or superhero-like comics did stay within the "reality like to our own" formula. I think all of these companies also saw the superhero genre as basically concerned with a basic fantasy of "fantastic beings in unfantastic surroundings" that goes counter to the more otherworldly SF/fantasy conceptions, not so much out of "various business considerations and weird historical quirks."
Here's the niggling part:
"DC has a set hierarchy in terms of which superheroes are the biggest deals, so you can't have a godlike supervillain like Black Adam just walk up to Batman and pull his head off"
But is it because of a hierarchy, or is it just a storytelling pattern that dictates, "Even when faced with an opponent far more powerful than he is, the hero will somehow dodge being automatically crushed long enough for him to turn the tables."
In the Campbell book I just mentioned, there's an Amerindian "fire-bringer" story in which Bear has the only fire-stone. The other animals conspire to get it from him, and they succeed, but since Bear is the strongest, the most innocuous animal, Swallow, has to approach Bear and pretend he only wants in Bear's tepee to get shelter from the cold.
Bear could, of course, squish Swallow as easily as Black Adam could de-cowl Batman the hard way.
But in both cases, if that "logical conclusion" were not excluded--
Then the story would be over in such a way that would please only Berthold Brecht.