Gamestop are giving customers back their preorder money, if this is a mistake then its a mistake on a completely unprecedented scale. Given the withdrawal of the product from their website and the expense of calling every preorder customer with a very precise explanation, it is clear that something has happened to trigger this.
They would not just misread something, decline to double check it, and happily abandon customer money, it contradicts pretty much everything I've ever heard about them as a business. I know they can make mistakes, obviously, but to be so happy to return preorder cash while its acquiring interest for them without checking the specifics seems an impossibility.
Likely scenarios:
-Format/distribution change. The Blu-Ray release of the PS3 Game "The Last Guardian" has been cancelled, and we will see the game in another form.
-The game itself has gone nowhere and development has been terminated, the company has cut its losses and informed the distributors in advance, with appropriate PR to follow to best manage the situation. Gamestop have done the unexpected/unforeseen and released the news early, and Sony HQ are scrambling to work out what to say. The responses "its not cancelled" are from reps not privvy to the cancellation of the game, or a desperate plea from an executive who doesn't know the PR plan.
Unlikely scenario
-Due to a random error on an email, Gamestop has seen the word CANCELLED next to The Last Guardian, and without doing any double checking of any sorts, gone to the expense of contacting every preorder customer to inform them and refund their preorder cash, losing a significant amount. They are happy to do this without confirmation from Sony.