Advisor: Japanese players are found on the Japanese website. Pokemon-TCG.com services all other countries participating in organized play.
From what I've heard, Walt Disney World and more importantly the Orlando area offers Pokemon Organized Play the best options for sanctioning and holding a large scale event. WDW offers endless options of activities, hotels, resturants, and shopping, that's excluding the multitude of places outside Disney property like the Universal Orlando Resort and International Drive.
I'd imagine, like someone mentioned above, contracts were signed to ensure availability for future Worlds. I'm assuming that Worlds will remain in Orlando until that contract is finished or a better deal is found elsewhere. That or if Japan offers to host it one year.
-Phil