ALL of them? As in every single one that they've ever made?
Wow.
Apparently the problem is the way they behave when max speed is achieved.
The thing is, hitting max speed on a self balancer physically means it can no longer balance itself. Balancing out a lean by the user, IS to accelerate. Simply maintaining speed is not enough, to keep a user that is tilted over, on-board, acceleration has to be occurring to offset gravity. If there is no more speed, then that also means there is no more acceleration. If the user is still leaning by this point, gravity wins.
EUCs solve this problem by keeping their electrical actual top speed far above the advertised top speed, and signaling to the user in some way when they ABSOLUTELY MUST STOP accelerating. Because once the hard limit of the voltage coming out of the battery is reached, the self balancing ceases.
OneWheels have pretty small batteries, and much lower top speeds than most EUCs. I'm not surprised a lot of people pushed the limits, and hit them. AFAIK, they don't have an audible signal that warns the user they are approaching max speed, either.