Nothing new about this.  But the fact he can be so sure means everything is moving according to the timeline.

Shacknews reported that according to Mike Morhaime (Blizzard Entertainment's CEO), Wrath of the Lich King will be released between October and December 2008.

"We have said that it will be coming out this year," Blizzard CEO Mike Morhaime revealed in a conference call today. "I can tell you it's not coming in the July to September quarter."

As for the Wrath of the Lich King beta, Morhaime noted that "testing is going very well." During the call, Morhaime also mentioned that 40% of the World of Warcraft subscribers that left for Age of Conan have since returned.

Source - Shacknews
http://www.shacknews.com/onearticle.x/53962

My bet is end Nov/Early Dec.  Dun think they can do it late Dec as too much work needed to be done just after launch and every1 is in holiday mood.