I think you are being told porkies.
Having just checked the ford website I can find no reference to what you have been told by the salesman.
As a matter of interest, though, you generally find that the service packages offered by dealers are excellent value. Certainly my last two dealerships for Honda and now VW are very good indeed and cover more than just the service with things like an additional period of vehicle recovery and tyre reolacement. In fact you will probably get more for your car when you come to get rid of it if the book has been stamped by a Ford dealer rather than another garage.