I believe the non-Cupa models do not have a mechanical diff. They only have electronics mimicking a differentsial working, by using traction control and braking on either of the front wheels. It's called an XDS electronic differential.
Official VW explanation:
The XDS electronic differential lock is an extension of the familiar EDL function. However, XDS responds not to loss of traction but to the unloading of the front wheel on the inside of the corner when cornering fast. XDS applies pressure from the ESC hydraulics to the inside wheel to prevent it from spinning. This improves traction and reduces the tendency to understeer. The level of pressure applied ranges from approximately 5 to 15 bar. The impression when driving is similar to that of a limited-slip differential in toned-down form. The precise, one-sided build-up of brake pressure makes cornering even sportier, quicker and more accurate.