Back when Pinball Expo had a banquet, with a keynote speaker, we heard from executives of many of those companies. In particular, the people from Atari and Allied Leisure both mentioned how they were disadvantaged by their respective non-Chicago locations. Among the impacts are the costs of shipping parts TO the factory and shipping finished games FROM a factory in a corner of the country to the distributors. There is also the issue of getting experienced workers.

ForceFlow's enumeration of companies in Chicago should have stated explicitly that both Stern Electronics and Stern Pinball were/are based there. Other Chicago-area companies: Exhibit Supply, Chicago Gaming, American Pinball, Midway, Bromley, Grand Products, Genco, and Keeney. Gene Cunningham's companies were in central Illinois. Spooky Pinball is close enough to Chicago to enjoy some of the benefits noted here.
.................David Marston