US mains voltages are less challenging than most of the rest of the world. Hence a preference for 400V input rated DSO's.
IMHO you are making a way too big deal out of this. When measuring mains like voltages you won't be using a standard 1:1 / 1:10 probe but a differential probe (if you are sane).
Well you don't sell scopes and like any seller I have NO IDEA of the expertise of a buyer not to make a simple FUB economic repair mistake by using 1:1 probes on elevated voltages that might make any product look bad. The first criteria I had for selecting a brand to sell was 400V rated inputs.
Result to date....no input damage of scopes I've sold.
If selecting a scope for myself with the experience I've gained, this criteria would matter less.
Hunt though the forum for scope repairs with damaged inputs, there's been a good few over the years.
How does this happen......elevated voltages.