The wisdom behind attaching the short (length) ground strap from the negative battery terminal to the bolt on the transmission is that the starter motor frame is the ground for the starter motor. The starter motor frame is bolted to the engine, the engine is bolted to the transmission, and voila the transmission is grounded to the negative battery terminal via the braided ground strap. Shortest path = least loss due to resistance and heat.
Grounding connections between the cab, fenders, other body parts and the frame will help the lights and peripheral stuff to have a good ground. The starter motor ALWAYS needs a low resistance (beefy connection, shortest distance) ground.
