B/X Known World
It doesn’t say that. What it says is: “Furthermore, it is usually essential to the character's survival to be exceptional (with a rating of 15 or above) in no fewer than two ability characteristics.”I always like to point people to the 1e AD&D PHB which says very clearly that a PC should have no less than two stats of 15 or higher.
“Usually essential” is not “no character shall have less than two 15s.”
Weird because exactly that method is a listed option in the DMG.People playing 3d6 straight were not playing the way Gygax was directing.