You're going from the thought that one could live for long enough to document the level over radio commands. At that point, if they could live for that long, the level would not be a Deadzone, but rather, a Class 5 or lower.
I think that people just can't understand how a scale works, they just need something above the scale to prove that their levels are dangerous. It's not like 5 is already high enough, they just need to keep going.