Dogs have the same issues as humans, many have food intolerances - not necessarily full blown allergies, but some have those as well - to wheat, soy and corn. Over time dogs can get skin and digestive issues. And lets not forget that dog food doesn't usually use organic, they use genetically modified versions, which can lead to increased tumor growth and cancer and other diseases. I'm not surprised so many dogs get cancer now a days, just like so many people are getting cancer now.
As much as I don't like the fact that Blue Buffalo advertises on TV their basic dog food, and I purchase Blue Wilderness, which is their premium food. I just looked on the Food Advisor site and the salmon flavor ranks at 6 starts and 5 stars for chicken. When you compare prices, Blue Wilderness seems to be the best value in premium dog food. I don't necessarily believe, you always get a better product when you spend more. Unfortunately at this time I can not spend any more on dog food. If I had more money, there are better foods than what I'm feeding my dog. I'm in the field of holistic nutrition, and when I adopted Atticus (my terrier) I spend about 6-8 hours total comparing dog food labels and reading about what an active breed like a terrier requires for fuel. I also feed him some raw veggies daily. He loves cucumbers, radishes, carrots, cabbage, kale stems, broccoli, cauliflower, and apples