Defogger Heater problems of the 1998 Audi A4

My heater recently quit blowing hot air. The vehicle has 75k000 miles and is less than 5 years old. I am told it is the heater core. This seems odd as a heater core should never go bad over a 5 year period. The labor is 14 hours or about $1,200. Then, I was made aware than the Audi dealer stocks heater cores. This seems even more odd as it should not be happening enough for the dealer to want to stock the part. I have had other things go wrong on the car and they almost never stock the part. This leads me to believe that this happens and awful lot. This part should not have that type of failure rate.