Maybe the reasoning is backwards? Given 4 limbs, how else would you layout an upright walking creature? The same across-the-chest muscle setup that makes us go

Maybe the reasoning is backwards? Given 4 limbs, how else would you layout an upright walking creature? The same across-the-chest muscle setup that makes us good at throwing also allows us to throw an effective punch. "push against the ground with your feet to exert significant force using your hand" must have many, many uses.