I have never seen a scale used at a poultry show so it is unlikely that a bird would ever be DQ\'d for weight deviations. Unless they weighed every bird in the show, you would have a pretty good case to dispute the DQ. If they did weigh all of the birds my guess is that a large number of bantams would be DQ\'d for being overweight, and a lot of LF birds would be DQ\'d for being underweight. I have seen comments on show cards that say \'Too Big\' or \'Too Small\' but these are purely subjective comments since the judges are not using scales.
That said, we as breeders should strive to get our birds as close to the standard weight as possible. If you have overweight Ameraucanas you are probably on the right track as I think most LF Ameraucanas are still a bit underweight.
Curtis