The decision as to when the new stadium would be ready for proper use was left until the last possible moment. At the time that it was taken (middle of June), Levy was assured that the new stadium would be ready. And indeed it would have been (ready, that is......not completed) had there not been a monumental fuckup with safety systems wiring that only came to light two months later.
As you say, things can and do go wrong on major construction projects. But Levy is not the kind of man to act impulsively or take wild punts. That much should be obvious by now. He will only have made the original decision on the basis of long and careful consideration of of the best available information at the time. Nevertheless, even the best laid plans.......
Reading this thread (though not referring to your post, I hasten to add), you would think that Levy and Spurs were guilty of torturing puppies or eating babies, such is the level of outrage that the switch of date and venue has caused. Yet, as Crouchino said above, Levy and Spurs wanted this outcome less than anyone. I fully understand the worries about the pitch (which apply every bit as much to Spurs) and the inconvenience and cost to fans (which also applies to Spurs) but I'm not sure what realistic alternatives there were.