The SAS plans have a MSRP just like the car. They also have an invoice price and dealer hold backs associated with them. I believe; however, am not sure that they count towards dealer sales incentive/bonus that is normally based on new car sales.
Joe, just appears to be willing to take a smaller cut of the difference between invoice and MSRP - maybe just keeping the hold back. In any event, I would say it is more similar to buying a TV or other equipment where there may be huge price differences between vendors.