Unfortunately, sounds like you're dealing with a typical Honda dealer...and one that knows that they don't have competition for a few miles. Unless they can show you in writing, I've got to think this nonsense of "if you only purchased from us" is just that. I've never heard of a non-selling dealer refusing to honor a warranty problem, regardless of make.
In my experience there is a difference in treatment between "premium" dealers and "standard" dealers, particularly with respect to service. The Audi story above echoes many others I've heard from friends who drive that make. Ditto Lexus, Infiniti, and Mercedes. Unfortunately...my wife recently bought an Acura, and we were
this close to an Audi...I was really rooting for the Teuton.

While the sales experience was great, it took less than a week to learn that the service dept. doesn't recognize the concept of premium branding. From logistics to QA, it's obvious we bought a Honda, no matter what it says on the decklid.
Anyway, sorry for the tangent. In your owner's manual you'll find a number for Honda of America Customer Service. I've got to think they'd be interested to hear about your recent experience, and offer a solution to the problem. Good luck!