You are ignoring one huge factor: culture.

The United States has culture of spending and spending. A big chunk of the middle class is in debt and has very little savings. We Americans love to have luxury material goods that we don't need such as Plasma-TVs and Sirus radios. The poor are like everyone else, they get a little bit of money and spend it on luxury items such as cars and shoes. The only difference is that the poor feel the effect of their spending more than middle-class.

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