When I got my 2000 (faclift) A3, I did not have the external temp reading. However, When I took the car into the Stealer for an Air-Bag recall, I asked them about it as the display is mentioned in the handbook.
When I picked the car up, hey presto, one external temprature display!! According the Stealer, as long as the car has Climate control, you can get them to 'turn it on'. I guess that anyone with access to VAG .com could do it too, but I've no idea how!!
Best thing was, I didn't even get charged!! /ubbthreads/images/graemlins/groovy.gif