In an article dated November 11, 2011, PC Gamer reported statistics for online sales of the The Witcher 2. According to PC Gamer, Direct2Drive, Impulse and Gamersgate's combined sales were a total of 10,000 (4%), GOG sold 40,000 copies (16%),[43] while Steam sold in same time period 200,000 copies (80%).
On February 20, 2013, Defender's Quest developer Lars Doucet revealed the first three months of revenue following his game's release across 6 different digital distribution platforms, including 4 major digital game distributors and 2 methods of purchasing and downloading the game directly from the developer. The results showed that GOG.com generated the second-most revenue of the 4 digital game distribution platforms used, trailing only Steam.
http://en.wikipedia.org/wiki/GOG.com