ARM CPU is not powerful enough. The cost of develop own version CPU can not be justified for long run. Yes, Apple ARM has the big volume for its tablet and iPhone. However, considering the cost of license fee to the ARMH, manufacture cost to the foundary, and its own CPU R&D cost. That's not good investment long term. Can Apple CPU team really overcome all the headache at the reasonable cost ? I serious doubt. The rumor of iPhone5 deal is actually caused the A5 CPU used in iPad2.