I think what they are saying is the money will be spent irregardless. If you and three friends go to a game this weekend you will spend ~$200 total on tickets/food/beer/parking etc. If you and three friends can't go to the game this weekend because there is no arena and sports team in the area ... you will go grab a case of beer and some snacks and rent a pontoon boat for the afternoon and spend ~$200. Economic impact = the same I think purchasing over the internet may be changing this assumption. Nowadays, people may still spend the same "entertainment" dollar amount, but it's no longer a Brewer game-related versus somewhere else in Milwaukee trade-off. Now the trade-off might be more Brewer-game related versus internet sales related, which i think would increase the economic impact of sports stadiums.
