Speed ... with the new Apple processors and the a I,it’s to do more complex and demanding things on the phone with the apps, especially the gaming apps, which are more powerful these days.
Indeed they are, they currently run games on iOS that were on XBox 360, such as Bioshock. Most games though, aren’t that powerful, and the controls on an iPad... Well, let’s just say it’s more practical to stick to your XBox console or PC for some of the games they are porting portable. No doubt the portable playing is a tribute to power, but using an iphone/iPad screen as an XBox controller is pretty bad.