I think because if you have spent the time training your dog properly it has a great bond with you and knows that you are "top dog" and respects you.
I am currently training our boy for the KC Gold award and I have been his handler from day 1 when we started puppy classes. I only ever have to ask him to do something once and he does it straight away, whereas my OH does occassionally let him get away with stuff so he is more of a challenge for my OH.
I say my boy has more respect for me than my OH...... they way it should be anyway LOL
