Its really not that expensive at all to move to a new phone. Normally you can sell your old phone so if you upgrade lets say every 2 years your looking at $500 every two years. If you finance it with your carrier its ~$25 a month. Pretty low cost for such a advanced and high usage device IMO.
25 a month for the phone (In Europe it's way more expensive for less than €40 a month no carrier will give me a new IPhone) and after that you have the additional costs. And yes it's made up by the market your phone only lasts for 2 years, just to sell more devices.....