While you think the herbal remedy may have "cured" your dog, be aware that in the vast majority of cases, kennel cough/bordatella will clear up all by itself in healthy dogs, with no intervention at all. Much like the common cold will clear up in healthy humans. You could have saved yourself $10.00
Also, there are a number of strains of bordatella, and the vac does not protect fully against each strain. Additionally, it is rare but not unheard of that a dog will get it as a vaccine reaction - so just because a dog was innoculated, there is no absolute guarantee that s/he can't get it.