Answer:
Using per capita income as an indicator of economic welfare shows the income for a "typical" person in an economy. This does not, however, show the full range of incomes. Some can be much higher and others can be significantly lower.
It can also be argued that using a form of income to determine welfare isn't entirely accurate because the quality of life (though it generally has a positive correlation with income) is not only measured by money. It is also measured by happiness, leisure time, and other social aspects.
Think of it this way: if Americans were to skip weekend breaks and continue production seven days a week, income would increase, but would that necessarily mean a better life?