During the E3 demonstration I noticed that the size of the pip boy screen they were using seems to be much larger than that of an iPhone 6+ yet those are said to be too large for the Pip Boy edition. Anyone have any idea how they managed to get such a large screen in the casing?

It does look a bit large but I think it's kind of an optical illusion thing.. Simply placing your phone on your wrist and you can see that your phone basically covers that. The phone then sits recessed behind a flared out rounded off square which gives it depth. Your brain then includes the outer ring as part of the screen even though it's not.