Tim Cook talked about trade-offs that currently exists that is prevent Apple from release an iPhone with a bigger screen. And until some of these trade-offs are addressed, that'll never happen. Some of these trade-offs are technical while others are related to the what kind of a mobile experience a 5" iPhone can bring to the user.
Let's focus on the technical ones here and discuss why I think that by releasing the iPhone 5 in the form factor it is in, Apple may have painted itself into a technical and design corner that is preventing it from releasing a 5" or bigger screen iPhone.
With each successive iPhone update, Apple focused on how they were able to shave off a few grams here and there while making the iPhones thinner and thinner. This was especially apparent with the iPhone 5 because it had a bigger 4" screen while managing to weigh considerably less.
Should Apple be thinking about a 5" iPhone, the expectation for thinner and lighter will remain. However, there is only so much Apple can continue to do that given the technical restraints. And this will be especially difficult with a 5" iPhone because of the battery that will be needed to power the light up the screen. It would also mean more pixels for a CPU to drive.
And even if Apple doesn't make a 5" iPhone thinner and lighter but keeps it around where the iPhone 5 is now, might may not be enough to give the iPhone user the same or greater level of mobile experience because of the battery constraint.
Maybe Apple will find a way to come close. However, had Apple kept the iPhone 5 thickness the same as the iPhone 4/4S, battery life for a 5" iPhone might not be an issue at all.
So, where does that leave us as far as a 5" iPhone goes? Well, Apple could reverse years of practice of releasing thinner and lighter iPhone and, in fact, maybe make the 5" iPhone thicker and heavier to commodate a bigger battery. Well, since this issue itself in the trade-off, it's not going to happen.
So, Apple has no choice but to wait until their engineers find a way to design a vastly more efficient CPU and more power friendly 5" Retina Display while accommodating Jony Ives' designs. It would also mean that we could be a year or more away from see such an iPhone.
Meanwhile, yes, Apple's competitors like Samsung and its Galaxy lines, from the S 4 to the Note, continue to sit unmolested by Apple's mobile devices. Sure, these devices have many of the trade-offs that Tim Cook is talking about but they are also sales that Apple is missing.
Personally, I would not want Apple to make compromises to the whole mobile experience. However, I think I am speaking for many Apple fans that if Apple does release a 5" iPhone that is slightly thicker and heavier than the iPhone 5, we would not mind at all.