This particular patent application was first filed late in 2012, which was not too long after TransparenTXT was introduced on the Windows Phone platform and Transparent Screen made an appearance on the Android platform. I suppose it has taken the USPTO approximately one and a half years to make sure that Apple’s patent happens to be valid and it does not violate any of the existing products out there in the market.
It would be interesting to figure out just how USPTO arrived at this particular conclusion, although it would seem strange if none of the other app developers thought of filing a patent on their work. It is all rather confusing for the layperson, as there are rules concerning prior art and so on, so hopefully light will be shed on the matter one of these days.