I always thought they were mainly a one trick pony.. the A4. The Porsche dealer in my area is also the Audi dealer. I am a long time customer of the Porsche side of the business and they always have A6 and A8's around but they are not very popular...yet. The SUV business is brisk.
As for myself, Audi is never on my radar. It's MB or BMW.
13 Mercedes CLS 550 4Matic
13 Mercedes E350 Coupe 4 Matic
13 Porsche 991S Cab PDK