Granted, this is ridiculous - I'm not buying sauces to top my dog's food, but I don't believe for a minute that an animal can't distinguish between different flavors. That's just silly. For one thing, I have a senior cat who is exceedingly picky about his flavors of canned foods (he can't eat the dry stuff anymore). We always have 2 or 3 cans in the fridge for him to chose from at mealtime. And if you saw the craziness that ensues with my dog when I get the ice cream container out of the freezer, you would never say that he can't taste different foods. He's insane over ice cream.
If vets say they can't differentiate between flavors, they are not a vet who understands animal behavior. Sure, they can survive on one type of food. So could we as long as it had the nutritional daily requirements. And if that is all they care about, I wouldn't have them as my animal's vet. My animals deserve the best I can give them. They give so much to me in return, it's the least I can do.
BC