The battery capacity comparison with the iPhone 4S misleading; you can't compare mAh from batteries with different output voltage. A battery with the same mAh rating and twice the voltage output would have twice the energy capacity - just like when you put two batteries in series.

For a fair comparison the mAh should be multiplied with the voltage output which will make it mWh. So to compare both, the iPhone 4S has a 5291 mWh battery and the Droid RAZR has 6650 mWh, making it a 1359 mWh difference.