I once had 160V on a properly wired 30A pedestal. The problem was a bad neutral in the CG 240/120V distribution system. My Progressive Industries HW50C shut down the power long before I could react. I've also found 3 cases of reverse polarity on a 30A CG plug. Plus numerous cases of low voltage especially in the summer with ACs running.
I've never had a problem with any 50A plug. Most 50A plugs are newer and the wiring is heavier. While many rigs can use the full power available in a 30A plug (3,600W) very very few rigs come close to using the full power of a 50A plug (12,000W).