All good points above.
Another consideration is that a quarter rib allows the builder to add a little weight and keep that weight more concentrated near the action between the hands.
Not sure which maker was first to quarter rib their bolt guns but Rigby was pretty early on with their 416s. Considering the use of the rear square bridge Mauser action, VonGruff's points make sense.
Also, Rigby rifles prior to magazine rifles often had "Rigby Flats" and Westleys often had the Knock form at the breech end of the barrel.