First things first - Theory Z is not a Mcgregor idea and as such is not Mcgregor's extension of his XY theory.
Theory Z was developed by not by Mcgregor, but by William Ouchi, in his book 1981 'Theory Z: How American management can Meet the Japanese Challenge'. William Ouchi is professor of management at UCLA, Los Angeles, and a board member of several large US organisations.
Theory Z is often referred to as the 'Japanese' management style, which is essentially what it is. It's interesting that Ouchi chose to name his model 'Theory Z', which apart from anything else tends to give the impression that it's a Mcgregor idea. One wonders if the idea was not considered strong enough to stand alone with a completely new name... Nevertheless, Theory Z essentially advocates a combination of all that's best about theory Y and modern Japanese management, which places a large amount of freedom and trust with workers, and assumes that workers have a strong loyalty and interest in team-working and the organisation.
Theory Z also places more reliance on the attitude and responsibilities of the workers, whereas Mcgregor's XY theory is mainly focused on management and motivation from the manager's and organisation's perspective. There is no doubt that Ouchi's Theory Z model offers excellent ideas, albeit it lacking the simple elegance of Mcgregor's model, which let's face it, thousands of organisations and managers around the world have still yet to embrace. For this reason, Theory Z may for some be like trying to manage the kitchen at the Ritz before mastering the ability to cook a decent fried breakfast.
Ouchi's Theory Z makes certain assumptions about workers. These include the assumption that workers tend to want to build cooperative and intimate working relationships with those that they work for and with, as well as the people that work for them. Also, Theory Z workers have a high need to be supported by the company, and highly value a working environment in which such things as family, cultures and traditions, and social institutions are regarded as equally important as the work itself. These types of workers have a very well developed sense of order, discipline, moral obligation to work hard, and a sense of cohesion with their fellow workers. Finally, Theory Z workers, it is assumed, can be trusted to do their jobs to their utmost ability, so long as management can be trusted to support them and look out for their well being.
One of the most important tenets of this theory is that management must have a high degree of confidence in its workers in order for this type of participative management to work. For this to work, employees must be very knowledgeable about the various issues of the company, as well as possessing the competence to make informed decisions.
Theory Z stresses the need for enabling workers to become generalists, rather than specialists, and to increase their knowledge of the company and its processes through job rotations and continual training. In fact, promotions tend to be slower in this type of setting, as workers are given a much longer opportunity to receive training, and more time to learn the intricacies of the company's operations. The desire, under this theory, is to develop a work force that has more of a loyalty towards staying with the company for an entire career, and be more permanent than in other types of settings. It is expected that once an employee does rise to a position of high level management, they will know a great deal more about the company and how it operates, and will be able to use Theory Z management theories effectively on the newer employees.
While several similarities and differences surround the ideas of McGregor and Ouchi, the most obvious comparison is that they both deal with perceptions and assumptions about people. These perceptions tend to take the form of how management views employees, while Ouchi's Theory Z takes this notion of perceptions a bit farther and talks about how the workers might perceive management.