Blizzard has nothing to worry about, Cataclysm is shaping up to be a defining expansion pack to make most MMORPG's jealous of. There is already an insane amount of new content and the quality is through the roof on most of it. The things I've experienced with phasing are actually pushing WoW into being able of delivering great story lines that other MMO's simply cannot due to 'static' restraints of their game worlds.
At this stage, everyone is freaking out and hyping up The Old Republic and Guild Wars 2 based on developer promises. Age of Conan and Warhammer Online both had a gigantic hype train and suffered from an overabundance of promises that the developers never kept. Age of Conan is finally just now recovering, Warhammer on the other hand is still suffering from "It will be awesome, but it will be implemented so terribly poor so it will really suck" syndrome.
Cataclysm is putting a massive effort into overhauling the new user experience, there will undoubtedly be an enormous increase in new player retention that the current game does not have. In all likelihood, I would not be surprised to see WoW surpass the 10 million mark again. Cataclysm is re-inventing WoW, it's not just another content expansion like Wrath of the Lich King felt.
I cannot understand what is up with all the negative hate towards Cataclysm, but I do understand most of it is coming from the same people that have repeatedly hyped up other games that haven't been successful.
As a last comment, SW:TOR caused a massive blow to myself and a few others I know that were passionately craving it when we saw they are trying to mimic the tank+healer+dps group synergy common to all MMORPG's. It was supposed to be an epic story driven multiplayer star wars game, hopefully similar to the other old republic games. I believe in the developers, but at the moment I already am not excited for a star wars game based on tank/heals/dps roles. Their healing role looked horrendously implemented.