when the vehicle hits the dealers lot, the manufacturer places a draft to the dealers Acceptance Corp. They are often but not always owned by that same manufacturer. Whoever the dealer is using for this "floor plan" is also likely to accept a lot of contracts from this dealer for leases and purchases. The dealer pays interest (pretty low) but the manufacturer provides the dealership with "dealer Assistance" which will often cover about 3 months of interest. That is why they don't like inventory sitting on the lot long.
Oh, and i avoid getting any type of service at a dealer if at all possible. My GF had to get her jetta its 40K miles service to keep her warrenty, she basically paid $400 for 2 new tires and a oil change...that's a bit of a rip off in my opinion.