I think Nolan's following the Batman movie tradition of basing the atmosphere of the story to fit a specific of Batman's career in the comics. It's what every major Batman film has done thus far. I mean, think about it:
Batman - 1930's era Batman (He used machine guns, killed criminals, and was more of a grim creature of the night)
Batman Returns - 40's era Batman (This Batman was pretty much the same, except for that it began to go 'out there' in some respects.)
Batman Forever - 50's era Batman (The first real era where Batman did outrageous things, like visit Mars and turn into Giant Apes. While this Batman didn't do that, the sets and the situations speak for themselves)
Batman & Robin - 60's era Batman (Batman and Robin being public figures, over the top villains and situations, ect... Need I say more?)
Batman Begins - 70's era Batman (The era where Batman regained his darker roots, Began journeying outside of Gotham City, and acknowledging a real world outside of Gotham. Also where Ra's Al Ghul first appeared)
So... that said... it's possible TDK will be in line with the 80's era of Batman. Which is damned good, as far as I'm concerned, considering the 80's brought us Year One, The Dark Knight Returns, and The Killing Joke, aswell as the first journeying into Bruce's psychosis.
I honestly wouldn't be surprised if TDK was intentionally darker, and Batman was a little meaner in this one. That combined with the characterisations of The Joker by both Alan Moore and Frank Miller of that era is getting me pumped for this, provided my theory is true. (Which I think is in part of Micheal Ulsan producing these films. He's the one that first brought this to my attention in interviews on the B89 special featurettes.)