People do all sorts of things with their engines. Not a whole lot use straight 30, but it used to be common in the older days. I would not go as far as he goes but I will say that we have gotten used to thinner multi-vis oils. In some other parts of the world like Australia and NZ the same engines we use are spec'd for much thicker grades of oil and the cars don't blow up. You see the used oil analysis on here, thinner oils are used in most PCM's and they wear great and last a long time if you maintain the whole vehicle. You can use a thicker oil but why do it? You here all kinds of crazy things on the internet. Stick to what the manufacturer calls for.