I have an 02 XL7, though I haven't had any issue in the rear brakes, I have also noticed minimal wear. I've towed nearly 2500#s with it across 3 states (KS, MO, IL) couple of times, have driven it daily for several years, have 112k miles on it now, and replaced for the 4th time, the front disc pads. I think I need a rotor(s) now as there seems to be some out-of-round effects in the steering and a little pumping action on the brake peddle while braking. I know one rotor is scared some.
I still buy rear brakes and compare the new ones to the old one, but it doesn't look like any wear. They have to be working as the surfaces are not rusty.