Actually it says:
If SAE 0W-20 is not available,
SAE 5W-20 oil may be used.
However, it must be replaced
with SAE 0W-20 at the next oil
change.
If you are savvy enough to get a Used Oil Analysis you might think it provides you with protection in case of engine failure but Toyota will be pointing you to the manufacturer of the oil if you need to file a claim. I have nothing against any particular brand of oil but I can afford the frequent oil changes other people claim they don't need. But claiming it's ok to run 30 weight oil is just more misinformation.
Forget all the "protection" talk and focus on hydrodynamics and the difference between forcing water through a garden hose versus forcing cold molasses through. The oil pump in the 5th Gen V6 was designed to run 20 weight oil max. The channels were designed to run 20 weight oil. The problem with thicker oil is that pressure builds up and pressure leads to leaks and leaks lead to failure. Is it as dramatic a difference as water and cold molasses? No usually, but time takes it's toll, as does high RPMs and hot weather. 0w-20 is the recommendation, why bother trying to second guess the people who designed the engine?
It's not a big surprise that you don't hear about engine failure due to the wrong oil. No one's going to want to admit to the world that they blew up their engine trying to save a few bucks. I mean, look how many people blamed Toyota when they jammed on the gas instead of the brake?