Well, I skimmed the site because I don't need to buy their book and read sensationalized claims to know the truth.
Yes, less than reputable companies put downed animals in the food. The word "rendered" basically means melted down anything - diseased cattle, etc. And it is true that some foods are the equivalent of giving your kid a multivitamin and then letting him eat twinkies 24/7 with no other source of nutrition. It is true that the "guaranteed analysis" measures protein, but the analysis won't tell you if the protein came from chicken meat or another less than desirable source. Yes foods like "Beneful" can claim to be complete and balanced and play to your senses by showing carrots and peas on the bag, when there is nothing complete or balanced about that food.
My suggestion, rather than read the book and scare yourself, is to first switch your dog to a REPUTABLE company - one you can't buy at Petsmart or the grocery store - like Canidae, Innova, Merrick or Orijen. Second, pay $20 and get a year's subscription to Whole Dog Journal.
www.whole-dog-journal.com