Why is everyone acting so surprised? Overshipping and underselling is quite common in this industry: Halo 3 had 7 million copies ready to go on day one but only managed to sell like 3 million copies in the first week. Fallout 3 shipped 4.7 million copies on week 1 but they didn't sell so many copies in one week. Sony simply chose to show the bigger number (shipped to retailers), that's all.
Currently playing on PS3: God of War III
Currently playing on Xbox360: Final Fantasy XIII
Currently playing on NDS: Chrono Trigger