Does this mean they're healthy? No. Their coat is usually falling out in clumps, they're obese they are slow and lethargic, blind, deaf and are constantly ill. Even if it isn't visible, most have been suffering from crippling arthritis for years. And their owners, steadfastly believing that Iams is the most premium food out there, just pump them full of anti-biotics, shots, and put them through multiple surgeries.
I think this is a minor exaggeration, as most old dogs I have known have been far, far from this description, and have been fed grocery store kibble for their whole lives. If the dog is doing well on the food, and the vet says the animal is healthy, there's no reason to change. (and in some cases the change can do harm)