There is an interesting trend in these numbers, especially when you compare them with last year. Last year, Nielsen claimed about 17 hours a week of playtime for WoW players, so playtime this year is actually down overall (and while we don't see month to month numbers, GameCyte says it was before the Wrath release, which makes sense). Sure, you could say that with dailies and the easier instances, players just don't have to play the game as much, but really, this seems to reflect the bigger trend: that WoW is leveling out.
There are probably years left in this game -- as we said on the podcast last week, the only real way people will stop playing WoW is when Blizzard finally turns the servers off. But all the numbers we've seen definitely point to a slowing down point among the game's subscribers. Lots of people (11.5 milion) are still playing World of Warcraft a lot. But not as much as they used to.