I personally think that educational establishments should use a range of operating systems that match what is used in the real world.
It's easy for the IT manager to specify the operating system that they, and their team, are comfortable with, but the aim of education is to prepare the student for life after they leave school, not to make things easy for the IT department.
At the current time that would involve running XP, win7, Vista, and OSX / Linux. When the student has graduated into the world of work they will then not be blinkered into expecting a particular OS and are more useful to their employer.
This would of course mean that the IT staff have to understand multiple operating systems, which should be a requirement for employment. We have a lot of establishments, (not just in Education), where the IT department is far more blinkered than the users, with many only having used XP in their career.