There is a slight difference here. The first step to hacking the Apple TV was the obvious one to remove the harddisk. With any computer, you can open it, remove the harddisk, plug it into another computer, modify it and put it back in. That will be a lot lot more difficult with the iPhone. It will be more difficult to open (it may be impossible to open at all), and it has flash memory inside - much more difficult to remove and modify in another computer. The second step was going through USB; the iPhone has no USB.