Stanford design prof Michael Shanks has an online course unit about the design, politics, sociology and economics of slot machines that is flat-out fascinating, especially the manipulative psychology of slot and casino design.
The layout also takes advantage of the differences between slot and table players. In general, table players do not like the noise of slot machines because they find it distracting. In addition, they may sometimes play a few rounds on slot machines spontaneously, but obviously prefer table playing. At the same time, however, spouses or partners of table players will often wile away time playing at a nearby slot machine. Thus casinos are planned such that there are slot machines lining walkways around tables. However, these slots are always tight. This cuts down on the noise and distraction to table players, and makes sense because the majority of players on these machines are playing spontaneously, with little expectation of winning. This demonstrates to what degree casino layouts are optimized–in this case, to the point that a complex system is implemented simply to clean up loose change from spontaneous players.
Update: Andy sez, "Just for accuracy's sake, the report on slot machines is actually a student project by William Choi and Antoine Sindhu."