Looking at Figure 4 in the original paper http://documents.worldbank.org/curated/en/914431468162277879/pdf/WPS6719.pdf it would appear that mature economies have a significantly smaller share of the 75th-90th% in 2008 than they did 1998 (huge drop in 17th ventile as example). In other words they have more people in the > 90th%. Is this due to people moving up in income in mature industries or due to their sample being smaller relatively over time?