i'd also like to suggest that the first sentence about the doubling cube be changed to, "Backgammon (and its variants) is the only game which can be defined as a match that employs a doubling cube."
as it is (saying that the game can be defined as a match with a doubling cube), it could be taken to mean that the doubling cube is somehow used to define the match. i'm a pretty smart guy, but it took me many readings of those rules and the playing of a match just to figure out that that wasn't what that first sentence meant.