If current trends and rates of Gentrifications (in Washington, D.C. about 12 blocks are "flipped" a year, for example) then the United States could very well find itself in 30-50 years with patterns of urban development completely opposite to what it is today. As land values increase in the city, then the urban poor may be displaced to where land is cheap and the cost of living low: today's outer suburbs, especially if energy prices continue to rise and commuting is no longer seen as economically viable.
Because housing is easily bought these days by poor, who are just clamoring to get the those houses. The housing market is booming by the way.
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