2004 BMW 530 Suspension torsion bar

I have a 2004 530I with 60,000 miles. I bought the car from a BMW dealership with 100,000 warranty. As I speak, its in the BMW dealer repair shop and I have been told that the torsion bar needs to be replaced at a cost of $730.00 and it is not covered because BMW says its a wearable part.

Firstly, I think its a very gray area that its a wearable part.
Secondly, if its a wearable part, why was it not replaced [like most parts] prior to the sale of a certified BMW car like other parts [brakes etc]. Cant have it both ways.

While I have agreed to have the dealership do the work, I will talk to the General Mgr. At the dealership. I would be interested to what everyone thinks about this situation.