here are some interesting points to note... talk time and standby time is much greater on the 928 vs the 920
Here are the two full spec pages, scroll down to the power management section for details on talk time and standby time...looks like their numbers could be for real and not just a mistake....batteries are different - similar capacity (2000mAh) but different voltages , 3.41V on the 928 vs 3.7V on the 920.
Could this mean a new or different SOC?