Think McFly Think
Release dates can make or break a movie. Studios congregate in their respective war rooms and strategize for the ideal release date for their particular films. Chinese food is ordered, profanities are bounced around the room, and grown men cry, until a decision is agreed upon. Not uncommon after such trials and tribulations the studio turns around and changes the release dates for one reason or another. They call it Hollyweird for a reason.
For The Brothers Warner in 2008 it was the WGA strike and the success of the previous Harry Potter film during the summer movie season, their new found love-affair with the mid/late July slot coming off the hugeness that was The Dark Knight (You might have heard about it) and need to fill in a release-date pot hole that allowed for the brain trust to move Harry Potter And The Half-Blood Prince from November 21st, 2008 to Summer 2009. When a big tentpole such as Potter is moved, other films from the same studio also have to be shuffled around. In addition, rival studios may react to the check with a checkmate of their own.