I'm sure it's standard on all S-tronic A3s now. Certainly my 2009 MY A3 has it and I did not order it as an option. If fact it is no longer listed as an option.
The description in the Owners Manual reads:
Driving away on a slope
The system is activated when you press and hold the brake pedal for a few seconds.
When you release the brake pedal the braking force will be maintained for a momemnt in order to hold the vehicle and make it easier for your to drive away.
As it seems to purely involve the braking system I see no reason why it cannot be fitted to a manual as well as an s-tronic.
Perhaps someone with a manual can check to see if their car has it fitted.