A lot of GM vehicles in Australia are marketed under the Holden brand. Granted, it's a little bit of a warmer climate, but 10w40 synthetic is readily available there. (And recommended by the Holden literature) Of course, they're not subject to the CAFE standards we have here in North America. I think GM just learned a hard lesson running 0w-20 in the brand new vehicles of the 6.2 that are all now recalled.... And now even GM is recommending the 40 weight in those.
It's worth noting that my wife's 2014 Escalade, they recommend 5W30. You had a co-workers 2014 Sierra pickup with the same engine, 0w 20 is recommended. It's in his owner's manual and printed on the oil cap. Different recommendations for the same engine, the only difference is the fuel economy standard they're trying to meet for two different models. When politics start dictating lubrication versus fuel economy, it's definitely not good.