If "monsters" are designed differently than "characters", then nothing stops you from designing an NPC either way. And no matter how simple you make characters, if they have any customization at all, the potential is there for overkill--whether random orc #3 with a bow, a shopkeeper, etc. So having this difference provides something highly useful that you simply cannot get any other way.
That said, the real key to this version, I think, is the nice side effect of having different levels of complexity for building/running the game. That shopkeeper could be built as a "monster"--quickly that way. Or it could be built as a "character" with a lot of options ignored--gnome wizard 1 + "merchant" theme (perhaps designed by you) and/or a couple of relevant "skills". Or maybe the base is simply a gnome commoner with some extra Int or Wis or Cha + "general dry goods merchant".
The stuff that is there to make PC customization as involved or not as you want, also means that the DM has multiple options for picking the base and combining that with options.