Have you ever been in a relationship that you just know is bad news, but you can't help but stay? Some call that being a glutton for punishment; for Apple, it's called smart business. Prior to the launch of the iPhone 5s, it was rumored that Apple was going to make the shift from Samsung to Taiwan's TSMC for chip production, but thanks to some reverse engineering conducted by Chipworks, it's being confirmed that for at least this generation, Apple has stuck by Samsung.
The reason this partnership is so interesting at this point in time is that in the mobile market, Samsung and Apple are fierce competitors. But from Apple's perspective, the move to a different fab for manufacturing is far from a small event. It needs to be done with care, because the absolute last thing a company of its size and product demand needs is a manufacturing problem that throws its release schedule all out of whack.
That being said, Apple would undoubtedly like to move away from Samsung, so a move to TSMC is likely to happen in the near-future - possibly for production of the iPhone 6.
Interestingly, Chipworks also discovered that the "motion" chip found in the 5s, dubbed M7, is also made by a third-party, NXP, which is a major win for that company.