It really warms my heart to see marketing-FUD crafted with this degree of care and attention to detail, and brings back fond memories of some expert practitioners in the field who I have had the pleasure to work with over the years.
For quite some time, the NEC has required campgrounds be wired to deliver an average of at least 33 amps for each 50 amp site, and 10 amps for each 30 amp site, with voltage drops calculated to be reasonable. The only way it's realistic to exceed this is at older campgrounds with few 50 amp sites, where the campground is quite full and everyone is running the A/C on a hot day.
Those are the scenarios we hear about.
You can get overvoltage one of two ways, either through the power company deliberately setting the line voltage a little hot to compensate for voltage drop somewhere farther away, or because of an unbalanced load in the campground itself, which can happen if the electrician who wired the campground didn't think through which posts to wire to which leg. Both situations are rare, in the U.S.
Then again so is low voltage, though maybe not as rare.