Either these people have outdoor dogs or the articles were written a long time ago when the quality of pet shampoo was very poor! (happytailsspa-blog.com)
If your dog has fairly normal skin, with no flakes, grease or excessive smell, using a natural pet shampoo is fine. (vetbabble.com)
This means a reduction of harmful chemicals and drugs associated with pet shampoos, flea and tick treatments, and other medications. (petsmagazine.com.sg)