The knowledge base is similar but not identical. The training focus can be quite different. Business school PhD programs are about 95% for the purpose of training business school faculty. If you don't go teach in a business school, you're a failure to those programs. Industrial Organizational Behaviour programs in stark contrast are developed in the scientist-practitioner model, the idea that all IOs should have a foot in both research and practice. It ends up producing graduates with very different philosophical approaches to research.