I wonder if dogs would have become domesticated if they knew someday they would only get dogfood.
Still, it's a lot better than cat food or fish food (how about vulture food). Remember what else dogs eat, they're not fussy.
Our last two or three dogs have all been self regulators -- their dishes always have food -- but it's always dog food. They do get their share of treats.
But I know they can tell the difference. My wife's brother stayed with us not too long ago and thought he'd be clever since he knew we don't eat meat. He bought a small bag of vegetarian dog food while he was here.
I don't know if it was the fact that it was veggie or just lousy but our dogs didn't care for it at all. Ha, ha.