A short history on the economics of pinball:
In 1986, Williams High Speed changed the economics of pinball forever. Pinball developers began to see how they could take advantage of programmable software to monitor, incentivize, and ultimately exploit the players. They had two instruments at their disposal: the score required for a free game, and the match probability. All pinball machines offer a replay to a player who beats some specified score. Pre-1986, the replay score was hard wired into the game unless the operator manually re-programmed the software. High Speed changed all that. It was pre-loaded with an algorithm that adjusted the replay score according to the distribution of scores on the specified machine over a specific time interval.
Of course, if you really want to understand the economics of having a pinball machine in the back of a grimy pub, you should read this and then this. And then you can shed a tear as you read about the final pinball company.