Although all projects follow basic phases, it's important to note that IT projects and engineering projects differ, for a few simple reasons. First, engineering is a discipline that is taught with very rigid standards that have been gathered for thousands of years. In fact, as you go through an engineering school, you will be taught project management implicitly because engineering projects are conducted according to well-designed plans. You don't start building a bridge without something written down. It just won't work.
IT, however, has a very different feel to it. Many of the people I meet each day in IT didn't start in the area and were not trained in it. Instead, they had extraordinary skills of some sort, and they often began as codersthat is, writers of the language for the machines. They then continued up the corporate ladder but often topped out as a group leader or lead technical person. For many, the next step is project management, and because most people don't take anything like project management topics in their undergraduate studies, PMI offers a way to become aware of and then competent in Project Management Practices.
Another major consideration in IT is that often a single "build" is done and then sent to the sponsor for approval. This means that often it is difficult to write a complete project plan because rework or sponsor input sometimes change the original schedule. This issue causes consternation among those who want project management to be a rigid science, as in the engineering realm. But in fact there is a major divide between IT and engineering that should be acknowledged even as we teach for the exam. The notion of an "agile" programming process originated conceptually as a response to the more rigid building standards of engineering, and it is becoming more and more important in the IT world. For this exam, most of the model describes a plan that is written at the beginning and followed to completion of the project. The original writers of PMBOK seem to have had an engineering frame of reference, and the book reflects it. Remember this point if you want to pass the exam, no matter what your area of project management.