Brake rotor question

[Brax Sisco]

I just recently had a garage put front brake pads on my '97 200SX.  I've
done brakes before, but this time it was easier to pay a garage than get
out in the cold and do it myself.  Car has 74000 miles, original rotors,
first time pads have been replaced.

The problem now is a rubbing, scraping sound brakes make at low speed
stops.  Garage says rotor has a "hard spot" on it and needs to be
replaced.  They said rotors are too thin to "turn" down.

Now, I thought brake pads were the wear item, and the rotors should last
a while.  Am I being lied to, or can 74000 miles wear the rotors down
that much?  Should I measure the rotor thickness?  What is the lower limit?

Thanks,

   Brax