playBunny: In chess I believe you play only single games and each game is worth 1 or 1/2 a point whereas in backgammon there are matches worth multiple points.

It's not as simple as that. The chess rating system works just fine over longer matches - in fact, it works even better. If the real rating of two players would be known, one could calculate by which margin a player would win (or lose). For instance, a rating may predict that one player would win 65% of the games. Obviously, this would never be possible in a single game (the score being one of 0%, 50% or 100%), but in a 10 game match, it certainly is possible to get 65%, or at least get closer to it than 50%. In chess, if players play a match of more than one game, or even a complete tournament, ratings aren't adjusted game-by-game, but the result of the entire match or tournament is used. So, if you play a match or tournament, and according to your rating, you should score 58%, but you only scored 45%, your rating will drop.