And herein lies an entirely different problem. As we agree that Tim Cook is currently making money, at what point do you replace him? When he stops making money or do you replace him before and take a risk on the new guy messing up the current set up?Yup, but even the shareholders or at least the investment bankers want to see Apple's next thing. They're relying on a single product line and if something happened to the iPhone, then all those earnings would disappear. This was the same complaint with MS with Windows/Office, most of the profits came from there and investors were worried.
So Cook has been great at managing the product and eking out every last cent from the iPhones, what is Apple going to do next - that's the thing. I'm not saying he's not able to do that, but rather with the iPhone product maturing and computer sales as a whole shrinking. They need to have other revenue sources.
To use a slightly ropey analogy, in UK football, your manager has got you in to the European places but he's not playing exciting football and there's no marquee signings being made. Keep him on the basis that he is technically successful or replace him cos you want to be Champions. Replace him and your team gets relegated then your fan base truly deserts you.