Apple made it so that new/updated apps have to be optimized for the iPhone 5, my question is that do these new apps have to be made for the 4s screen etc.
I discovered today that if you load "Icon.png" into a UIImage,
you end up having loaded the icon file that the device is currently using,
so if the 114x114 icon was loaded, it's a retina display.
Silly, but should be more future proof than looking for models.
It probably would work with Default.png as well to identify the screen size,
and again, not the done thing, but appears to work.
Are you using Xcode 4 or 5? I'm going to guess 4. You should use 5, it handles this kind of thing better.
Silly, but should be more future proof than looking for models.
Not sure how that's more future-proof. iOS 7 already requires 120x120 app icons.