Folks, to think there are not extra cost for pets is not reasonable... Many parks are setting aside space for pet areas, provide bags for poop pick up, carry insurance relative to dogs. Based on what we have experienced there are incidences where dogs do damage to the grounds due to negligent pet owners. So the question is do the campground owners eat the cost, pass it on to all their customers or charge those with pets a fee?
Realistically, I think most of the fees charged are arbitrary and not consistent with the model of cost recovery. The reality its "what ever the dogs will eat "meaning what ever we are willing to pay. In some cases it is a nuisance fee designed to discourage pets. Fortunately in most venues there are choices...
The same arbitrary and apparently capricious tack on fees come into play for extra people, children, visitors. The reality is that these campground owners have a sizable investment and any leverage they can get on their investment without compromising their volume of visitors is fair game... No different from any other business.
JohnnyT