They're partially correct: even upgrading Windows (or whatever) where the apps stay largely the same is a major exercise. Compound that with re-education issues, and you have a major headache.

BUT re-education is a one-off cost only if your support technicians are sufficiently educated to be able to support your users - and are you really going to fire all your Windows staff who also know all sorts of other company-related info? So you need to get your techs to be at least one step ahead of the users.

It costs.