I believe the GameStop by my house said they need at least 45 preorders to do a midnight release on any game, and even if they meet those numbers they still often do not do midnight releases. Midnight releases cost the employer money, as they have to have workers stay after hours, usually resulting in overtime.
We are usually told when we have our midnight releases because the company has to assign hours to a store for them. They can't just do it without corporate saying so. Number of pre-orders does not matter.