Distribution plot depicted as area graph

http://www.gapminder.org/downloads/income-distribution-2003
The distribution plot here is a two-way graph, with “Number of people” on the Y-axis (vertical) and “Income per year” on the X-axis (horizontal). There is an extra dimension represented by the size of the area. The distribution plots are also sometimes depicted as area graphs, more times than not, to make the visualisation appealing to the audience. It is of course sensible to do so since the information is carried by the area under the curves. However, the shading of the area is redundant and may obstruct the view of the entire distribution