Interesting, I'm not too clued upon the S3's or Golf R's, but I got this from the A3 wikipedia page, there's a section about the S3:
"
Although dubbed "quattro", the S3 uses a different "on-demand" four-wheel drive system.[2] The Haldex Traction coupling adjusts the bias of torque distribution from the front to rear axle as grip requirements change - most of the time it operates as a front-wheel drive"
Could be something to do with loss of power in the drivetrains?
