The 19-21 column is mainly for reference if a magical effect takes a characteristic above 18.
For me 'Looks' is also a general indicator of good health and immune system - so high or low looks also impacts other physical traits such as health and perception (in terms of eyesight and hearing). It's not arbitrary, but rather based on
science.
But mainly to make it less of a dump stat in vanilla DW.
I have not added many non-canon skills to this to maintain compatibility to vanilla DW, hence the lack of 'social skills'. At most I have tweaked existing skills a little, and added 5 'characteristic' abilities (Agility, Charisma, Concentration, Endurance & Willpower) that are broad 'improvements' for characters wishing to specialise in any general skills that rely on characteristic tests. There are also a few others (a couple for the 'Sage' profession, and a few general add-ons mainly for Barbarians such as expert swimmer and horse archery).
This is actually a stripped down edition of a full upgrade to DW that I used in the past. For this version I removed everything that wasn't compatible with vanilla DW, hence some of the mistakes in the text where I missed necessary tweaks and adjustments from my original, more expansive, 'house rules'.