I drive a 2005 2500HD Chevy Silverado 4 door. Its not a work truck by any means and is mainly driven by my wife back and forth to work. Other than her full time job, she helps a local dealership process car deals and paperwork. I have the luxury of getting her employee discount on all my car maintence and in a recent discussion with the service manager says for trucks its a must, (flush and filter change) about every 30 to 40k, but for cars not so much.(we also have a GTO ) THis guy is not out to make money as the discount brings the cost down to where the dealership does not make much (if any) money. It sounds to me like they just want to make an extra $140.00, but ill be glad to give him a call tommorow and get his opinion for you.
EDIT: My apologies, i didnt see your post showing you found your answer