It's quite clear that depending on some vendor who can dictate what to do for the education system is a bad idea. And entities like MS clearly have that power now to some degree (or strive to gain that power). So using open source in education field is a natural way to avoid that. As I said, some actually get it enough to act on it. I don't think anyone thinks that it's good to have that dependency in general, most just don't go anywhere further than realizing that it's not good.