I also think it has ALOT to do with the quality of protein...Many of the foods that are out there are not good quality and contain lots of by-products and such...If the protein that they are eating is not very digestible, then the liver and kidneys are going to work very hard which can cause problems for the dog...BUT if dogs are being fed high quality protein, then the liver and kidneys won't have to work as hard...Following is a link that explains all of this in depth. Another thing that this article mentions is the fact that dogs need more moisture in their diet;therefore, it is recommended that they are fed at least SOME wet food or homecooked meals.
Here's the link:
http://www.dogfoodproject.com/index....e=protein_myth
Also, I want to add that everyone has to make their own choices, and not all dogs are the same.
Some dogs, like my yorkie, require low, non-animal protein as he does have liver problems...
Just like people, different dogs need different things