What people don't seem to understand with the upgrade program is that it's a 20 month agreement. You're just restarting the 20 month agreement every year, meaning eventually, at some point, you'll have to pay the 20 month cost, so you'll pay more.
How else would Apple possibly make any money?
The 20 month cost is the same as paying full price for the phone and ac and as you get to keep the phone what difference does it make?