"Straps are a lot tougher than folks give them credit for. "
I agree that the straps have the strength to hold the tractor. However they are not very durable compared to a chain. A tractor with a leaking tire will strap down nice and tight. As you drive the tire goes soft and the strap will loosen. Then every bump and stop/start cycle the tractor will move just a bit. Every movement will cut a few strands of the strap. It really does not take much to cut a strap with tension on it.
As to the statements that the trucker do it so it must be OK. There are a least 2 problems with that statement. First there are companies that do not supply chains and binders for the driver to use when they should. Second there are a lot of lazy truck drivers. Straps are lighter and easier to throw across a load so they use them instead of a chain.
If you watch as you drive the interstate look at the trucks that are carrying I-beams. Often they use straps. And those that do use straps do not use corner protectors. Everything works OK until it does not. The edge of an I-beam will cut a strap in less then a blink of an eye. Most truckers no longer place a chain across the front of the load to prevent the I-beams from shifting forward.
My dad was a volunteer fireman/EMT for over 50 years. He came in from a run one morning and was acting strange. A truck load of I-beams was involved in a wreck on the interstate. Strapped down and
without the cross chains. The driver did not make it.
Most 4 inch straps that are used on a truck are rated at " 4 inch Ratchet Straps are rated for 5,400 lb to 5,670 lb working load limits. "
Look at the trucks that are hauling similar types of freight. A new tractor in a crate gets strapped down. A rolling tractor gets chained.
