I wouldn't doubt you will see more of things like this when you are talking about long term stays. There are numerous incentives for RV Parks to move as many income streams as possible off of site rental and into additional charges. It allows them to advertise the site rental at a lower number (similar to how every hotel in Las Vegas advertises a low room rate and then adds a $30.00+ nightly resort fee) which is advantageous because many people make their decisions on the advertised cost, rather than the final costs.
It may also be that site fees are subjected to lodging taxes and utility fees are not. That would actually work in favor of the renter. Same with franchise fees. For example KOA charges a 10 percent franchise fee on site rentals, but not on additional people charges, additional vehicle charges, and probably utility charges as well.
But it very difficult to actually meter and charge utilities on short term stays, so this is only going to be an issue for long termers.