I see your point. But you are assuming people think this way, or know there actually is a difference in quality of food. When I was growing up, Purina was the end-all-be-all, and that's what we fed. These days, I wouldn't feed Purina to a rat!
The problem is, so many people think that if a food is AAFCO certified, it's good. They don't realize there is a difference in quality, and that AAFCO certification means nothing. And that the better quality the food, the better the results.
The problem is education, just like so many other things in life. There is a sore lack of education, and vets, who
should be able to advise their clients are poorly educated in nutrition, as well. So even asking the average vet is useless.
For more info on how to properly feed your dog, see this link:
http://www.bornfreeusa.org/facts.php?p=359&more=1 There are more links out there, but this is the best one I have bookmarked!
