So Retina Display is any resolution of 300ppi or finer, right? What are the Pixel-Per-Inch specs of the new Retina 15-Inch MacBook Pros, The New iPad (Gen3), and the iPhone 4/4S? It seems the PPI of the devices is not readily available and I'm sure someone here knows. Just want to get a feel for the difference between all three. Thanx.