There's definitely market segmentation and it's definitely a conscious decision, but there are other functional differences between the supermarkets. (Bigger package sizes at pak-n-save, and New World's are also located in more convenient locations).

So they probably got the market segmentation right. Compare with eg Four Square -> small, expensive, small selection, but still feels cheap.

I worked at New World when I was a kid and they definitely hired disabled and people of various cultures. I think this is reflective of the location of the particular supermarkets though. They are generally staffed with people from the local area so definitely represent the local demographic.