@SupaPhly part of the reason could be that they are more responsive to FOREX fluctuations than MS or Valve. The other reason is that we are so small for Sony that they can't be bothered to match what happens on the other platforms.
If you have both consoles it allows you to price shop, i've picked up a few games this way.
Uncharted follows the adventures of daring thief Nathan Drake who is in search of ancient ruins, priceless artefacts, and untold riches. Sony's Uncharted series has sold nearly four million copies to date. Known for breathtaking action sequences, deep and inventive mystery, and amiable characters, Uncharted makes its natural leap to print, much to the excitement of fans everywhere.