I'd much rather have a synthetic oil, which I know will withstand higher temperatures without beginning the breakdown process. Dino oils begin this process at a lower temp. I choose synthetics for my bike because they can withstand higher operating temperatures better, plus they hold up longer, resulting in longer change intervals. In my car, I still run high quality Dino oil, as the operating temps are relatively contstant on the high end.
You're overlooking something in this quote. While you correctly point out that synthetics handle higher temps without breakdown, you then say it's the
constancy of car operating temps that makes dino acceptable. It's not a question of constant; rather, it's the max temperature (well, and shear pressure too, but syn is still better) reached. Even with water cooling, car engines operate at high temps--we just aren't as aware of it, since we're not right above the engine--and no, I'm not going to sit on my car's intake manifold for a 5 minute traffic light in 90 deg heat to show it's cooler than my bike!