Though many Americans prefer the suburbs, I am not sure your West Los Angeles example is the best. Seems like LA continues to grow, and it grows most dense on the west side. So out of the 300+ million, many people like living in cities. In general, the city population of the US is pretty stable, growth in Los Angeles, San Francisco and New York more than offsets the decline in Detroit and Cleveland - we will know more after the 2010 Census comes out, but the percentage of the US population living in cities has stayed pretty constant since 1990.
Suburbs are gaining in population share, but surprisingly, its the rural share of the population that is declining - a decline that would be even greater if places on the rural fringe of cities was excluded.