I think I see the issue here more or less. It's part of an advertising gimmick and they were hoping that by releasing the demo early to Gamestop employees that they would use that information to help promote the product, and get people hyped up for the game. If everyone has access to it immediatly, there is less hype involved. This becomes counter productive when the demo (or employee numbers or whatever to download it) can be easily distributed, and probably will be by the employees. This basically amounts to releasing the demo early without any benefits, so they probably just decided to go with the original release date they planned.
Of course there could be other issues involved as well, such as wanting an extra week to work on compadibility issues, or remove a piece of content their in-house censors decided was too extreme at the last minute. Or it could just be the rumor that people who play the demo have an odd habit of winding up dead, but we've been informed it's untrue, and if it was it would be unrelated to the games so it's no big deal, and as you know I trust the game industry implicitly in all things. There is no such thing as the "EA Curse" or a thing called "Baron" manifesting through video games. Besides, who ever heard of a supernatural event with in-game dialogue being replaced with archaic french, and that seems to primarily target children. That's just plain silly. >.> <.<