That's a good suggestion, but based on the number of posts I see on various RV forums by folks that were surprised by a park's policy when they went to cancel a reservation, I suspect it would be difficult to entice all but the most dedicated reviewers to include that information. They'd likely have to research it first, something they apparently didn't bother to do before making their reservation. Add to that the parks that change their policy seasonally, and it starts to get even more difficult to accurately include. Perhaps it could be added to the editable park features list, so that someone that knows or is willing to look up the policy could add it, rather than asking for it in each review. And welcome to the forum!
Because reservation/cancellation policies are usually a bit complex, and frequently changing, it is always best to look at the park's website or call them for this information