It’s not, because the statement is much more accurate in the case of internet-connected devices, and for emergency messages it’s enough to have someone around you who has one (e.g. a neighbour). I guess it would be really hard to find someone - in the areas where this change is made - who doesn’t have access to such a device in that sense, maybe even impossible.
It’s really more like assuming everyone breathes air because most people do.
You do know landlines are still a thing, right?