So after watching the keynote I didn't really get a good grasp on how apps will work with (now) 4 different iPhone screen sizes. I am aware that if nothing is done to an existing app, the 6 and 6+ will scale the 4" version to fit on their screens, and 3.5" devices will continue to use apps specific to their screens. What I am more confused about is how apps will be going forward. Will developers be able to alter their apps for each of the screen sizes? So, for example an app on the 6 might have a UI that is slightly different than that on a 6+ and on a 5s. Or will the 6 and 6+ be bunched into the same category so that developers only need to develop one app that applies to both of the larger screens? I think this is a pretty important question to answer before purchasing one of these devices.