WOOOSH. His point was that in hotter climates you want a higher viscosity oil due to higher temps resulting in greater viscosity reduction. Towing in Vancouver vs towing in south Texas, for example, one would be more inclined to run a higher viscosity oil in south Texas due to the heat.
Further... 20 is far from "pretty thick." Product data sheets make that clear. My bike calls for 40 weights, the mower/blower for 30. Why would I want less protection for a modern engine? For .5 MPG? I'll stick with my 30s and 40s.
FWIW, I'm an auto tech. The number of vehicles I service DAILY using xw20 oils that are 1-2 quarts low or more is staggering. From the Korean makes, to American domestics, to Japanese. Most of our clients with German cars still have them spec'd for 30 or 40 weight. And some newer RAMs and Jeeps are spec'd for xw40 euro. There's a LOT of merit to thicker and very little for thinner. Maybe some makes/engines are fine on a 20, but I think you're rolling the dice. Engines are expensive and can take a while for problems to develop. Remember that.