[j_coder]

It is the opposite. Batteries degradation acts as an internal resistance at rest (Rd) that increases over time. There is a second resistance (Rc) that increases as you discharge the battery. As you draw current (I) from the battery the nominal voltage decreases according to Omhs law V = Vn - I*(Rd + Rc).

You can plot different voltage charts as the battery discharges at different stages of degradation (increased Rb). As you know the peak current that phone drains at maximum load you know the minimum voltage it requires to operate. At this minimum voltage you show 0% (or a little higher so the phone can have enough power to gracefully shutdown).

What Apple is doing is slowing down the processor so it drains a smaller current reducing the minimum voltage the phone needs to operate extending the battery life (that also measures the time between 100% to 0%). This way you don't complain that an one year old phone battery is discharging too fast probably because of battery fault or wrong specification. There also a good side effect for Apple of decreased performance perception that induces to premature phone upgrades.