In all honesty I got bitten by it yesterday as well on a VW Polo (same thing as an Audi, also VAG group).
Tried it by the main menu option but that didn't clear the service message. Went to the group 17 Instruments and tried it from there. Even though this car uses km's, It took me to reset all options, also in miles, before the reset really was done. It worked, but I am not sure what triggered it to work.
Will try to get some testing done on this shortly (next week or so). Too busy now. Also could not change the data (edit function on bottom was grayed out) to change mileage before service etc. Weird, this did work before if I remember well (normally I just reset, that's enough)