Remember this gem from Artie Ziff?
http://www.telegraph.co.uk/sport/football/teams/sunderland/8947206/Sunderlands-new-manager-Martin-ONeill-wants-team-to-play-the-Barcelona-way.html
It's clear that they give away that many free tickets that most of those that leave early don't have a) any interest and b) haven't made a financial commitment to buying the tickets which will give a degree of stubbornness.