Answering the question what Fincher did to earn his credit, director Andrew Stanton had this to say in a recent interview:
"It was his DP Harry Savides who did a lot of Gus van Sant movies that I was looking at at the time. And I loved how he used the camera for shallow focus on the stuff. And then he made this sort of intimacy with the camera—even in these sort of urban blight settings. And I thought, "That's perfect, 'cause I'm in a world where it's dystopian, and you've got these two metal boxes fall in love. Where am I going to get the intimacy? I'll do it with the camera." So I wanted to sort of talk to Harry Savides about that..."
Duh ...and all this time I was thinking Fincher might have been the one to suggest to make it a love story instead of an all-out space battle action flick...
Here's another follow-up read on this from New York Magazine:
So How Come David Fincher Got a Special Thanks in the Credits of Wall-E, Anyway?