Keep in mind that the migration from 24fps film to 60cps video has already happened when the DVD is produced. When the DVD master is created from that 24fps film source, part of the process involves developing 10 interlaced frames of video from every four frames of film. (There's an example of this near the middle of this Secrets article .) As far as the DVD player is concerned, every disc it gets is 480i at 60 cycles per second (or 30 complete frames, more or less). When the video output is kept at 480i, that initial "trick" of video mastering performed before the DVD was created will remain unaltered and the player has nothing to do. It's not the best solution, of course, but it's the only one that works reasonably with 480i/60 from a 24fps source.

When we give the player a chance to generate a 480p signal, we are offering the player a chance to correct some of the limitations imposed by going from 24fps to 480i/60 - which is both blessing (improved picture quality) and curse (opportunity to screw up that improvement). The player is going attempt to create 60 complete video frames, using alternately three and two copies of each original film frame (10 complete frames for each 4 originals).