I've seen this feature described on web pages for A3 outside of North America:

"Audi hill hold assist helps the driver perform a hill start. When the foot brake is pressed for some time when stationary, the braking pressure that has been built up is retained momentarily after the foot brake is released. Thanks to this automatic brake intervention, the system makes it easier to perform a hill start without rolling backwards."

My A3 rolls, so I am trying to figure out of this is available on the N.A. models, or if it just doesn't work. I'm using DSG in standard drive ('D') mode. Thanks.