All this debate over NPCs....
The truth is we DMs have always made them however we pleased. And always will.
Sometimes that means we roll some dice. Sometimes we just pick #s. Other times we just make up some modifier on the fly if needed.
But the crucial fact is that the DM can only make these decisions if he knows the context.
The DM could say that this halfling dressmaker has Dex 3 and Str 20, and describe her as 'weak but nimble', but the numbers are at odds with that concept.
The numbers are the way the game rules interact with the concepts. The numbers and the concepts should match.
In order to understand the meaning of Str 20 or Dex 3, you need a context.
In every iteration of D&D, that context is and has always been the 3d6 bell curve. That context has never changed.