I genuinely don't thing the average Singaporean knows that cases like the ones PNGMK highlights exist.
The government has been alluding to this recently. Your typical Singaporean is streamed in school from a very early age. Their friends are almost always educated to a similar level and get similar types of jobs. If you're, say, smart enough to get to university, it is very unlikely that you are going to mix of on a day-to-day basis with an odd-job labourer. And your neighbours at home, by definition, are going to be people with similar levels of wealth.
It's probably only when you see an old man sifting through the bins, that you even think that there might be another side to Singapore. But even then, I don't think there is full understanding. I've been warned not to buy tissues because the person selling "only pays about 5c per pack at Watson's, you know. They're making very good money". And I've had arguments with my wife about just giving our old newspapers to the garang guni man "because garang guni men are very rich what".
This all said, I'm a 'rich' expat and live in my own ivory tower, so I'm hardly one to moralise here.