There's an interview at MMORPG.com with Bruce Woodcock of MMOGChart.com. He elaborates on his methodolgy, a game's lifecycle and a future projection on the World of Warcraft subscriber numbers:

Through doing these projections, Bruce has noticed a pattern in a game’s lifecycle. Most retail games follow the same pattern: they have a rapid rise for the first 1-2 years, level out for 2-4 years, then begin to decline. If the game has a poor launch (but a lot of hype), this “cycle” is often compressed into a single year or two. Some games are different, especially those that are digitally distributed such as EVE – these games seem to have a slow growth over time. Does that make digital distribution healthier for the long-term MMO? Too soon to know!One of Bruce’s future predictions is that World of Warcraft will hit 12 million subscribers in the next two years – let’s see if it comes true!

His charts were also updated the 10th of April.