I'm not sure what res they did the CGI special effects stuff at for Episodes II and III, but the most important thing is that the movie itself is only 1k. Since The Phantom Menace was scanned in at 2k, they may well have done the CGI part of the special effects at that res, or they may have done it at 4k. Because when a Star Wars movie is shown at theaters you want as much detail as you can get in the special effects to match up with the inherent detail you get with real film in the movie.

LordVader: haha :) Yeah, Lucas did go overboard with the CGI stuff in Episodes II and III.