Thematic Maps: Gapminder started out visualising the data with a standard thematic map of the world which they colored to show changing variables like rise in GDP. Hans said they soon rejected that as countries with big areas such as Australia dominate the view visually. That's a clever insight IMHO.
Map with Symbols: So they tried circle symbols and varied their sizes. This was better but a change in size isn't as visually arresting as movement. Hans's smart phrase was : 'movement has a direct highway to the brain'. So they ended up with their famous graph visualisation and a map tab you can click to see a map presentation. I think the key point about the data presentation is that country location isn't that important, all you really need to know is which continent a country is in. This means the map can be ditched in favour of a graph plot which brings with it the advantages of movement and the ability to draw tracks.
I couldn't help thinking that Hans the statistician seems to know more about good graphical and map design than a lot of GeoWeb developers and GIS specialists I know.
Happy Easter Break!