New Achievement rules allow more Gamerscore per game
Microsoft has apparently upped the Gamerscore limit an Xbox 360 game can award a player, with the maximum now standing at 1,750 GS and 80 Achievements for a full retail game.
The previous limit was 1,250, set in 2007.
DLC GS is also limited, according to this Xbox360Achievements.org piece, to 250 and ten Achievements per quarter.
Thanks, Kotaku.