Most people equate marketing with sales and promotion with public relations. But marketing is a much broader strategy than just sales. It is the entire approach to how you establish your "brand," whether you are an individual or an organization. Most corporations have a detailed marketing plan, but unfortunately many entrepreneurs do not. Writing a marketing piece is very subtle and loaded with lots of implications and emotional qualities. The tendency is to be overwrought, for example "We're the best." Who says? Can you prove it?
Public relations is the art of getting free publicity and controlling the media when a crisis occurs. IABC has a whole seminar on crisis management. Public relations involves media contacts, special events, annual meetings, public appearances, etc. more than just writing a news release.