Do you know where these stats are derived from? We have found the slowest times to be January and in November before Thanksgiving. This chart suggests that the weeks before X-mas is the lowest attendance. We went this past December and found the crowd levels to be equal to springtime non-vacation.
The Passporter books have an excellent graph that depicts park attendance, the "seasons' for the resorts (value, etc.), as well as the average air and water temperature... all in one place.
I honestly don't find the scottware chart to be a very accurate resource. Nowhere on the site do they post when the last time it was updated and statistics have changed quite a lot since I first saw this chart online several years ago. They also indicate that Super Bowl Sunday is one of the slowest days in the parks, and that is definitely not the case.