"Why can't I just use my own shampoo on my dog? It has lots of moisturizers and it smells nice?"
A dog's skin is simply different than their human's. Our pH is more acidic than theirs and our shampoo is formulated for that acidity. So using your shampoo can actually harm your dog's skin by stripping away natural oils and setting up an environment for bacteria to grow. It can set up a wicked cycle: you wash your dog with your shampoo - your dog's skin gets irritated - bacteria moves in - your dog's starts scratching - a slightly "off" smell develops - you wash them again.
For more info: http://www.petmd.com/dog/grooming/evr_dg_shampoo_for_dogs