Just going back to this because you referred to it. If this is your understanding than it is fundamentally wrong and it's no wonder you can't wrap your head around how it works. The first number is the oil viscosity rating when tested cold. (aka "Winter viscosity"). The second is the oil viscosity rating when tested at 100c. They both measure the same thing at different temperatures. The AMSOil article you linked to explains this, as does the article I linked to. The oil viscosity changes as it gets hotter.Label: 5W/40
The first bracket of info on the label is the viscosity or 'weight' of an oil. When you see a W on a viscosity rating (The first bracket of info on a label) it means that this oil viscosity has been tested at a Colder temperature, aka: Winter Viscosity. A lower rating means it'll flow faster through the engine during initial ignition at start up. So lower is better. But once the engine gets up to normal running temps (approx. 100C) this rating soon becomes irrelevant.
The second bracket of info is about how long the oil will remain within working temps. 30 is fine for colder / most climates, 40 is better for hotter climates. And by climates, I also mean internal engine temperatures. So a 40 graded oil means it'll protect the engine at higher running temps (100C) better then a 30. If you live in Australia, or ride quite aggressively, then maybe think about a higher graded oil.
If you expect to run at outside temperatures that are so extreme that you would cause your engine to run at abnormally high or low temperatures, then you might want to adjust the oil viscosity you choose up and down. The reality of riding is that we all tend to do it in a fairly narrow range of temperatures and modern water-cooled engines with thermostatically activated cooling fans and other neat gadgets are really good at keeping internal operating temperatures quite consistent when riding within the engines normal operating envelope and most people's riding temperature tolerances. There was a time when all engines suffered from the effects of outside temperature and driving/riding style. Today, unless you're really riding at the extremes, these factors are pretty negligible in terms of the effect on the internal operating temperatures of the engine, which is why I don't worry about changing oil grades in different seasons, etc. You used to have to think about this stuff a lot. Today you really don't and lots of people overthink it.