Ok but only games that support the code for this controller will work. So the sellers of the controller need to make an app themselves. And it has to be a big enough hit for other devs to start supporting the controller. I'm all for seeing a controller attachment for games, that'd be awesome. But I don't think it will be as soon as you'd think.
Also if different companies make their own pad add-ons you might have to do different things to your app for each game, there might not be one single method of applying pad controls to your app easily.
Yet I think there very well could be a joystick controller, or a dpad style controller which perhaps emulates wasd and some other keys. This would make it a lot easier to use (you wouldn't need any special SDK or code).
Good replys, thanks. I was more thinking as to the possibility of using existing hardware (maybe a PS2 pad) with just an iPhone cable connector, or something similar. would make it easier, cheaper, and thus more mass market.