The argument could be made both ways. While I was watching Slumdog, I noted how grainy some of the images looked. An artifact of using fairly small digital cameras. I wasn't even watching it on a particularly large screen either, and I don't consider myself an expert in resolution.
Another huge part of cinematography is the lighting design, and one could argue that TDK had a lot more of it than Slumdog, and had a much harder time with it because of the IMAX cameras. You can't hide any lights in the periphery, because the IMAX camera would get them into the shot. Slumdog was basically shot on the run, aside from the game show sequences, and they wouldn't have had to set up much lighting for that.
But I think Slumdog and TDK are both fairly atypical in terms of Oscar-type cinematography. Benjamin Button would have been more up their alley.
Anyways, since TDK was at least nominated in cinematography, that's good enough for me. Everyone votes on the winners, and as we saw with some of the Slumdog wins today, the Academy doesn't know what the heck it's doing with some of the tech awards.

I have the feeling TDK juuuuust beat out Slumdog for that sound editing award too.