Apple could be working on a physical controller for its iOS platform devices - including iPad and iPhones - but it's uncertain whether it will ever be released. At least this was the case, according to a short section of text in an Anantech iPad review that appears to be getting blown up into an international news story.
While touch screen interfaces are perfect for certain game types, they don't exactly lend themselves to speed. There is also the problem on smaller devices like the iPhone, that as long as you're controlling something with your finger, it's often in the way of seeing what's going on. This has been solved in some titles by utilising a virtual analogue stick, but it's far from perfect.
One issue to consider with a controller system though is how do you view the game at the same time? Either the tablet/phone would need to be built into the controller - in the style of Nintendo's upcoming Wii U touch screen controllers - or it'd need to come with some sort of stand. But who wants to try and play an iPhone game at a distance?
While Apple's closed system approach means this will never happen, one option it could take is to open the iOS to third party manufacturers - in a similar fashion to Google's Android. By allowing other companies to produce their own controllers, Apple could see what works and what doesn't. From there it either makes its own, or more likely buys up whatever company produces the best product and makes it official.