Obviously, none of you have ever worked on software.
Something you have with movies: marketing strategy when it comes to release time. With games (and software in general) it's whenever you can get it on shelves. That's the way the software industry works.
When building movie schedules, directors and producers plan for problems based on past experiences. Ptoblems in the movie industry are predictable. In software, there are so many variables, there's no way in hell you can account for all of them. It's just plain impossible.
Software timetables look like this:
Code, code, code, release code.
Build content, content, fix code bugs, content, code bugs, content, code bugs.
Testing, fix content bugs, fix code bugs, more tetsing, fix, test, fix, test, fix.
You can write up a 5 billion page manual on how to make your release date, and you still won't make it. Why? Because bug fixes aren't always five minute syntax changes, they sometimes take days or weeks to fix because of faulty architecture.
In the movie industry, you have a story that is set, a video camera that you know works, and a crew of digital special effects people who make models and textures and computer animations with software that they know works.
When coding software, you're dependant on stuff that hasn't even been created yet. You have to create your own level editor, your own scripting language, your own 3d renderer. And once you have that all done, you have to build your own levels, which uncovers problems in your rendering engine, which leads to bug fixes and architecture changes.
With movies, you have a solid base of working tools to get you through. With software, you're developing your own tools, often from the ground up.
I know this because I write software for a living, and I can tell you that the best way to estimate when you're going to be done is to say what you think, add 50%, and then expect to slip, because you will.
Half-Life 2 has a brand new engine working on brand new technology being driven by brand new video cards that use brand new drivers. They're not working with pixar to create a couple models and animate them through a movie. They're creating a 3D world that is interactive. A world where YOU have control. The only control you have in movies is fast forward, rewind and play.
Games are much more complex and take a lot more time to develop than movies. The two aren't even comparable.