Not only was it incumbent on them to warn their customers, repair and replace.... It's The Law.
Can anyone think of a reason why Audi wouldn't inform their customers of this potentially dangerous problem if, by law, they had to repair or replace (even outside of the manufacturers warranty)? Here's a totally wild idea, they didn't want to spend the money to repair or replace! And if you got killed because you didn't know there was a crack in your frame, HEY WHO CARES! They are making that $$$$$ right?
Imagine you are driving on the highway with a cracked frame and you are going 70 MPH and the frame zippers all the way up and fails, you lose control of the car you crash. You're dead. You hit someone else's car. That driver is dead, their child in the backseat is dead. Hey who cares right? The Executives are making that $$$$$$$$$$. Huh? Is this seriously your position? I don't want to hurl insults. But seriously rethink your position Mr. desperado. Also, the law that is in effect right now (at least in Georgia) disagrees with you.
The fact is a frame should not crack during normal use. The frame isn't a "maintenance" item. You don't replace it, or do anything to maintain it. It should last for the life of the vehicle under forseeable usage conditions, i.e., driving on public roads and highways. The fact is the design of the passenger side strut tower is defective. There is a reason the driver side strut tower doesn't suffer this same failure. It's because the windshield wiper motor is installed via a beam which intersects the driver side strut tower, reinforcing it. There is no similar reinforcement on the passenger side and thus, the forces exerted on that frame intersection causes the frame to crack open, because it wasn't properly designed. I.e., design defect.