What do you call Iron Works if it isn't 'luck'?
Iron Works doesn't have as big an effect as the ToZ. Yes, it CAN if it happens right in your or an AI's core, but chances are it won't happen at all, or if it does, its in a crappy city.
However, at least ONE Civ is guarenteed a shot at ToZ. The ivory can be an any part of your empire and you can build the ToZ in your core. So, basically one Civ is guarenteed the ability to build the ToZ. The worst thing that can happen regarding the ToZ is that it is built a little late because the Civ that has the Ivory is in a war and cannot build it (which happened in my game).