I have used a browser on iOS, but I haven't seen a real ZUI there. Maybe one level like Mission Control. Maps is a different thing, there is just the map. There aren't a lot of things you are trying to organize in space, they have already been organized for you. You aren't going to be able to move your city closer to another, because it's more convenient. There's a difference between an object that is too big to see all at once, and a zooming UI for organization. Nor is it really revolutionary.