I was thinking the other day, and I ran upon this train of thought: The interview that says James was a chaser came out before OotP or the PS/SS movie did. Is it possible that JK changed her mind between then and now?
She's done it before. Michael Corner was a Hufflepuff in her original notes, but when he entered the book, he was a Ravenclaw.
She's allowed to change her mind. What if she did?
Also, J.K. reads the scripts for the movies, right? Why would she let them put something incorrect into the movie? [edit: I meant something incorrect that was apparent from the scripts, and not part of special effects. (that werewolf was utter blasphemy)]
[Edit: Another thought: Maybe he started out as a seeker, and as he grew older and didn't have so much of a "seeker" build, he "graduated" to chaser? Granted, there's no indication in canon that players switch out of the seeker position when they get too big, but again, just a thought.]
Just a random thought I wanted to share with you all