I just think that with DC, their legacy is too big for their own good. Marvel's heroes didn't come around until the 60s, so DC had a good 20-30 years to establish Superman and Batman before then. The fanbases for those two characters has become so ridiculous, that some DC fans treat them more like family members than fiction characters. That's why there's such overwhelming positive or negative reactions to the movies.
As for why fan worship "Dark Knight", they were just glad they got a great Batman movie after nearly a decade of suffering from "Batman & Robin". Although that doesn't let DC off the hook for Steel, Jonah Hex, Green Lantern, Catwoman and any Superman movie not directed by Richard Donner!