There are various sources of Internet usage statistics — one of the most easily accessible (but maybe not necessarily the most reliable) is this site, Internet World Stats. As all digital games — not only virtual role-playing worlds — are increasingly transforming into online services, it becomes increasingly important for game studies to follow what is taking place in the use of Internet.
Miniwatts Marketing Group (2000–2008) “Internet World Stats”. Online: http://www.internetworldstats.com/stats.htm
An Introduction to Game Studies 