Jackal: He's been a franchisee for over 20 years without this being an issue, it's only now becoming a problem.
Here's a real world example: Pizza Hut has a Taco Pizza, but not all Pizza Huts offer it. I'd think that the same discretion they exercise should be available to this small business owner. As long as the food he DOES serve meets the franchise requirements, I see no conflict, plus the fact that there are many Dunkin Donuts (three in his area alone) that don't serve these sandwiches, the argument that they are a 'Core item' doesn't seem to hold up.