Originally Posted by JARblue

Generally speaking, "warped" rotors (or excess pad deposits) are caused by poor braking habits. If you inherit one from someone else, get it turned, and then use your brakes properly, you should be good to go for the life of the rotors.

Since a person bringing their vehicle into a shop for this problem isn't likely to change their braking habits (and will probably get offended if their braking habits are criticized), its easier for the shop to simply not offer the service and recommend new rotors. Undoubtedly, though, the customer will have the same problem down the road after about 20K miles, which is long enough for them to not link the problem to their driving.