First - Warner Bros. Pictures Group President Jeff Robinov in The Wall Street Journal:
Mr. Robinov wants his next pack of superhero movies to be bathed in the same brooding tone as "The Dark Knight." Creatively, he sees exploring the evil side to characters as the key to unlocking some of Warner Bros.' DC properties. "We're going to try to go dark to the extent that the characters allow it," he says. That goes for the company's Superman franchise as well.
Source of for the original comment, one which has been repeated - often - by the current production staff.
Thomas Tull '92 Discusses His Journey From Hamilton to Hollywood
Thomas Tull '92, founder, chairman and CEO of Legendary Pictures (the company jointly responsible for producing the films Batman Begins, Superman Returns and 300), spoke to Hamilton students on April 17 in Wellin Hall about his journey from Hamilton to film production. Tull expressed appreciation for Hamilton's impact on establishing his success, and reciprocated by screening never-before-seen footage of Legendary Pictures' upcoming Batman sequel, The Dark Knight.
Legendary's roster of upcoming films includes a wide variety of properties, including Watchmen (from the renowned graphic novel), Akira (a remake of the popular Japanese anime film), a Superman sequel (in Which Tull hopes to invoke more of the image of "an angry god")....
And - many of the early plot/origin elements come out of the Superman: Birthright