I think I found his article: https://web.archive.org/web/20020604000533/http://www.suntimes.com/output/eb-feature/cst-ftr-ebert14.html
Sunday I was able to see the digital version, and Lucas is right: "Star Wars: Episode II--Attack of the Clones" is sharper, crisper, brighter and punchier on digital than on film.
This will come as melancholy news, I suppose, to the vast majority of fans destined to see the movie through a standard film projector. Although an accurate count is hard to come by, there are apparently about 20 screens in America showing "Episode II" via digital projector, and about 3,000 showing it on film. Lucas is so eager to promote his vision of the digital future that he is willing to penalize his audience, just to prove a point.
My feeling is that movies shot on digital video look better projected on video, and that movies shot on film look better projected on film. Of course every theater, every print and every projector is different, so results may vary.
What I dislike about Lucas' approach is that he wants to change the entire world of film to suit his convenience. Because his movies are created largely on computers, it suits him to project them digitally.
It seems he didn't necessarily say that Lucas made the film version deliberately bad, though.