The Xbox Man on 05 May 2010
There are various reasons, I believe it ranges from game & gamestation having an easter sale which reduced the price of FF13 to £25 (other games are undergoing this sales to, god of war 3 is at £30). Then you have word of mouth, advertising and a general drought of games right now. Combined these reasons are leading to what you see.
However I'm not sure about your GFK Full price chart comment, do they not count games sold under a "sale"? If they don't then it has more to do with word of mouth/advertising/incentives.
