Time to expand to more stores, ioi, so you're sampling can get better. It appears the PS3/PS2 numbers were right on the money, but the Wii/DS/360 numbers suffered the big percentage differences, and the PSP/GBA were within a reasonable disparity.
Perhaps the stores you collect from don't favor the Wii and 360 much.
Threads of Interest:
The Movie Thread: http://www.vgchartz.com/forum/thread.php?id=6880
The Crow Eating Thread: http://www.vgchartz.com/forum/thread.php?start=0&id=3886
The Betting Thread: http://www.vgchartz.com/forum/thread.php?start=0&id=7104
Custom GIFs Thread: http://www.vgchartz.com/forum/thread.php?id=18963
The Greatest Game Ever Conceived On Any Platform
Tag: "I have tasted Obi-Wan's bitter tears"