Why do organizations need to employ project management separate from regular management of the departments in the organization? Isn't the management of production (manufacturing) of products and serv

Why do organizations need to employ project management separate from regular management of the departments in the organization?  Isn't the management of production (manufacturing) of products and services and the business functions that support production enough?  

As you formulate your thoughts on this topic, you might wish to first think about what a project is and how it is different from regular ongoing activities.  Here are a few projects I am thinking of: building a house, obtaining a college degree, developing a new model of the Apple I-Phone, sending people to Mars, writing a book.

Why would we need special project management activities for one of these projects?  How can Project Management help us in situations such as these?

What are your thoughts on this topic?