Considering there was a transaction of money for the promise of a delivery it sure as hell is a binding contract where I come from. But true, my knowledge ends with my countries borders. Here, this is really not much different then ordering anything online. Two parties agree to terms, both are bound to fullfill these. That is the definition of a contract, here at least. From buying a pack of bubblegum to a sports car all fall under that category.
We fullfilled our part by paying the demanded sum, now Blizzard has to deliver the product by the date that was in the contract ever since Blizzcon (31st of Dec). If they can't or won't the contract becomes null and void and we have the right to a refund.
For other more essential items or items that we expected to sell or use for commerce of our own there would be the option to sue for the financial damage we suffered for the delay, but of course you would require a really good lawyer to explain why not having the game causes you financial or physical damage.