Im on the side that says that is the risk you take, and agree to, when making the reservation. I've had to cancel in the past and yes, I've lost a day's rate. All part of the process/system.
I also believe in being as up front and honest as possible. I'd hate to think just because I wanted to play games and 'pay' the Campground back for following their rules, that someone else couldn't take advantage of the site. So what if they were able to re-rent the spot out.
I actually had reservations at a campground that did not require a deposit at all. Just my word I'd be there. I called them anyways when I had to cancel. I could have just let it go.. not losing any money, but I called anyways. Seems like the ethical thing to do and possibly free it up for someone else.
I have also found that many places will give you a raincheck, even if it is not part of their official policy. As long as you are decent about it, and not being a butthead, you will be amazed at what is possible.
Mike