Which makes it all the more likely that we will see a big one for Wrath of the Lich King. Bornakk says that while Blizzard realizes that a lot needs to go into creating a big world event, they've also learned a lot from Brewfest and the Hallow's End events about how to both tune the scale and get players involved. But Blizzard still wants to do a big one, and from what we heard at BlizzCon, they're going to come up with a reason for Alliance and Horde to head up to Northrend after Arthas.
My guess? Arthas is going to become a threat again-- he'll invade Undercity, or bomb Darnassus, or somehow attack our world. And for the first time that I can think of since the game has started, we're going to actually lose something-- an NPC, a city (at the very least, Dalaran) or something else. For all of the fighting going on in the world of Warcraft, it hasn't yet changed that much. And I think that with the next expansion, Blizzard is looking to have Arthas shake things up a bit.