I can see his point. As a businessperson, he and his siblings have to think about the resale value of the team. Since the Cubs are one of the few (if not the only, I don't know the situation at all other 29 parks) teams with significant parking revenue, they need to make it up somehow. The reason for this is because all the MLB teams will, in the next few years, get into lucrative televsion/media contracts. For the Cubs to remain financially competitive without the benefit of 10,000+ cars parking in their lots 81 days a year, they need the revenues from in-game advertising. While you can say the Ricketts have all the money in the world, when it comes time to sell the team, potential buyers will want a team that have enough revenue streams so they can compete financially with the other clubs.
All hail The Rick