You forgot to mention that people also want to travel or that they want to buy expensive stuff - cars, TVs... These things cost the same for everyone, but a poorly paid employee has to save many more months than a well payed one.
For example, people from high income areas travel to where others get lower income and enjoy they vacation that also might save them some money, whereas others must actually save money for several months to be able to pay for such a VAC.
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