The Project Management Institute's (PMI) process of maintaining your PMP status insures that people who maintain their PMP credential continue to develop and evolve their PM skills. The PMP is the entry point for most people to being a professional in Project Management. The PMBOK continues to evolve as the entire community develops and evolves their PM skills. This evolution is incremental though so earning your PMP before the exam changes with the PMBOK 5th edition is less material - and will require less effort. But the real development as a PMP happens as you practice being a PMP and continue to grow your capabilities as a PMP.
Please feel free to ask Cheetah Learning anything related to the PMP as they are the training and certification efforts and have been personally involved in six exam changes.