I think Keith has it right. Part of the idea is yha each person comes up with a semi-definitive list. No sense having people change their lists.
i wrote a reply a while a go but it got lost in the tubes, this isn't about people changing their lists, or as _Keith_ suggests, going against an "actual list" and "actual tastes".
again, take my Top 20 ballot that had Top 100 representation in only 2 films. does this mean that i only like 2 of those Top 100 films? of course not. does the Top 100 do a good job of reflecting how these films resonate with the filmspotting community? again, i'd say no.
of those Top 100 films (or extend that to the Top 150 or 200), i think there were a handful that i would say i really like/love, but my interest in those films is not represented in the list, or in my initial Top 20 list. by having a second round, i would then change my ballot to reflect both my initial choices as well as the suggestions of others. i did not include Chungking Express
in my Top 20, but that does not mean i don't love the film; it might even be a sometimes Top 20 film. by casting a second ballot and placing CE
on my list, i am refining the representation of how filmspotters generally rank films. further, take something like Yi Yi
that just missed the cut-off, this might inspire folks to include it in their lists or prop it up to a higher position.