As I understand it, draws are suppose to affect ratings. I don't think many usually see it since it affects it less then a win/lose, and if the rating are some-what close to each other, you won't see any change.

But for example you have a player rated 1000, and another player rated 2000 - for the 1000 rated player to not lose and get a draw will get them some points.

I'm not sure of the exact formula, but I was thinking it was posted somewhere.