By making this an iOS exclusive, you're excluding oer 70% of the mobile marketspace that runs Android. Ignoring the small number of people on Windows Phone and Blackberry, you're ignoring a huge portion of people who use the single most popular mobile operating system.
As someoneone who has bought every Elder Scrolls and Fallout game as soon as they came out starting with TES III: Morrowind, I'm seriously considering not buying Fallout 4 because of this. Yes I get that you only have a small number of target devices with Apple and that reduces cost, but realistically, you could have just focused on the flagship phones from the major manufacturers of Android devices and had a similar number of target devices.
If you wanted to increase hype for the game, releasing this on a platform that most people don't use isn't going to do it.