I remember some speculation a while back that movement was only needed to cross a hex boundary. The movement cost of terrain was in essense the toll payed to cross that boundary. If the Magic Kingom is a hex, and Portal Park is at its center, those entering and leaving the Magic Kingdom are essentially cheating. Since they do not actually crossing hex boundary, they need no move to do so. Since casters are bypassing the hex boundaries, they can come and go as they please, even when it is not their turn. I don't remember who wrote it, but it made sense to me at the time.
मृत्युः सर्वहरश्चाहमुद्भवश्च भविष्यताम् ।