Judging by the comments I get from customers, I am certain that it's more than a theory. I've had a lot more people tell me that they "come here because it's always clean" more than tell me that I put out a good product (And I do, far better than anyone else in at least a 5-mile radius). Also, on any given nice weekday it's not unusual for all the bays to be busy at some point of the day, and people don't want to wait for a bay. They may use a muddy one and be dissatisfied, or they may just go elsewhere, and I'd rather not have either situation happen because some jerk spent $2 just to knock off some mud.
That's my theory, and I'm sticking to it.