The chart represents 1967 to 2011 and shows a timeline which includes recessions.
In 1967 the United States had a rating significantly lower than now. Much on par with other world economic powers. During this time the American middle class enjoyed and participated in economic growth.
Note the dip during the 70s recession and prior to the most recent recession. Which indicates wealthier people did not gain just prior to the recession. Further, note the increases during periods when Reagan and George Bush (1) were in office. The greater wealth reflected since 2008 is exaggerated due to economic downturn which has impacted the working and middle class of America.
According to the most recent CIA and Census data; at this time the United states has a rating much like the income disparity of the following countries: Mexico, Argentina, Ecuador, Venezuela, China, Malaysia, Sri Lanka, Cameroon, Mozambique, Uganda, and Ivory Coast.
To say the economic policies of the recent past are working for the American middle class would be a mistake if you look closely at this and other economic data.