You know this is the same problem that I had with Gary when we went through his first class. At Petsmart they are on a positive reinforcement program and corrections only go as far as a no, ah ah, or a squirt with a bottle or shake of a plastic bottle with some pennies in it. For many dogs that is all it takes to teach them what is expected...for thick headed stubborn strong will powered dogs that just isn't enough!
I tried and tried doing strictly only the positive reinforcement and I was getting nowhere with the leash walking thing. Now I am training at a different place where I have been taught how to use a prong collar and leash corrections for training and OH MY GOSH what a difference in my dog! I am to the point now (very proud of this, and my trainer noticed it in class tonight too) that I can walk around with the leash over my neck and have Gary stay in a heel with me even if I zig zag around the room. It is amazing!
So my opinion is that no, pure positive training does not ALWAYS work. It depends on your dog. My girl Zumi was trained on pure positive and learned to heel using a gentle leader. She was a very easy dog. Gary is so much different, I guess because he is a Rottweiler
