I'm not sure what you're asking. Apple has demonstrated time and again that their strategy depends on offering the best possible technology at desirable price points. Consumers don't care about MHz the way they used to, but they know the difference between a fast and slow UI, and they care about the features and battery life that are dependent on an ever more powerful and efficient SoC.

Intel, as much as they might want to please Apple and know what a coup it would be to be inside the iPhone and iPad, is only one company, and one with a history of engineering pride, sometimes to their detriment (see Itanium[1]). Apple would have to be sure that Intel would respond to whatever crazy demands their engineers come up with, and right now a bunch of scrappy ARM vendors seem much more likely to do that. If one fails Apple, they can hire another one for the next device. Worst case scenario: they can buy one. If Intel stops playing ball, they'd be stuck with another painful ISA transition. They've gotten better at those but they're not free.

Apple's seen what happens when a supplier roadmap (Motorola/IBM's PPC) goes out of alignment with theirs. Even if Intel produced a product at parity with the best ARMs, a competitive ARM market (albeit one currently dominated by Samsung) serves Apple better than a single source.

EDIT: [1] I should mention that Itanium was actually fairly effective for Intel at clearing the field of several major "enterprise" architectural competitors, disaster though it was as a real product. But surely they would have been happier if it had actually been a success instead of a multibillion dollar embarrassment.