Well, I think that it all depends on how you use the brakes. Do you crawl up behind someone then brake hard or do you coast in with more stop time. Brakes exchange kinetic energy for heat. The heat is caused by friction. The longer the period of time that you dissapate the energy over, the less friction you will require. In addion (just saw this again today in the holiday traffic), when creeping up on someone on the highway, do you let off and let the wind drag slow you down or do you touch your brakes. I was behind someone who was touching the brakes for a second about every 5 seconds on a downhill when the car in front of them was at least 10 car lenghs ahead. Definately someone who will be replacing brakes sooner.
In addition, the dealer will be very conservative about when the pads are replaced. They first mentioned changing them at the 45K service. At the 60 they said that it was "critical". I got another 10K out of the front and 15K from the rears before they were really starting to get thin. I checked them at the 45K mark and they were barely under 1/2. Now, if this was my race car, I would definately pitch them at 50% because there isn't enough material to dissapate the heat and the brakes will generally boil the fluid and fade once the pads get under 50%, but a street vehicle should almost never be subjected to that kind of heat load.