It's worth remembering that the "Revenue" number would count bitcoins twice if they were used in two transactions. If bitcoins used to buy something on the site were then used by the seller to buy something else, the revenue would be twice the total bitcoins used.
According to this that's close to the current total supply of all bitcoins:
http://en.wikipedia.org/wiki/File:Total_bitcoins_over_time.p...
The graph shows the supply in 2013 at around 9.5 million, same number as what the article claims.