Ship On Time With Success 101

I often wondered why the game industry lacks when it comes to shipping dates of their products compared to other mediums such as music and movies. I know developers spend ages coding and designing the games to get them out to the consumer and as anything software related, dates can slip provided you don’t have a stable set of code. I am all too aware of this. So what are some things that could cause this? Is the marketing team speaking out of turn when they give a release date? Is bad planning and execution being done by the developers? Why can’t this industry market their product with a solid date so the consumer can just walk in the store on a Tuesday and pick up their new copy of X game? Does it even matter if the game sells even if it’s late? Why am I even bitching about it?