I’m pretty sure it’s because the amount of people putting in orders. Just like with anything on release date, there is always a huge influx at the beginning because everyone has to have the newest and greatest. With everyone ordering, they are going to ship them in the order that the orders are received. So if you were to log in right away and be the first one to order then you would get yours right away. As the queue builds up, it’s going to be further and further out because they are going to have to fulfill all the orders that came in before yours. That date they give is when the first orders will be shipped out.