The oil film depth has to be equal to the task at hand. A turbo-charged truck engine living at 4,500 RPM (gas) under load and pulling a grade (say a contractor truck with a trailer) may very well need a 40 grade oil because of heat.
Average motor designed between WW-II and 2009 needs 30 grade for most circumstances. Only with CNC/laser checked and robotic manufacturing processes have the clearances come down to the point where a 20 Grade is usable, or preferable in non-winter temps.
Back specs are iffy. If the Grade was correct at 30 when it was built, the engineers will likely still prefer a 30. The Gov't analysts and the bean counters and the corp lawyers who have to deal with Gov't may want something else and may out-vote the engineers ...
Singapore is generally a lot warmer on average than much of the USA. Yes, we get similar temps in the summer, but they stay that way year round. So many of their engines are quite happy on 30-40-50 Grade oils. As stated, they don't even look at the W rating. It's meaningless to them.
And, it's very likely that oil is either costly, or from dubious sources. So they may be making up for inferior chemistry by adding base film strength.
And to answer the question above about 5 seconds of cold start - it never was "flow" that protected your engine. It was always the existing film strength/viscosity. Many parts of a motor never see pumped oil in 200,000 miles and they run fine. Piston skirts, cam chains, cylinder walls, distributor gears, etc. They all live on splash or slung oil and always have. Even parts of the vale train may not be lubed by pumped oil.
If you've ever been to a County Fair where they have a lotto on how long an engine will run w/o oil, most folks loose their money big time. That residual oil film is very durable and lasts into the 20~30 minute range unless they drain the coolant too. In which case the engine fails from heat seizure, not lubrication failure ...
This whole concept of flow equals protection is bogus in the extreme. Even journal bearings that get pumped oil, only take what the need to make a full film. The rest is side leakage. That may be useful in and of itself as the cylinders and the cam are lubricated by slung oil off the crankshaft. But enough is sufficient. And they are always wet on start-up with residual oil from yesterday.
The question to ask for start-up concerns is which oil maintains best film over night ... And teh answer is often not a full synthetic ...