I know that there is a problem on the IS220 with the rear brake calipers.
They seize or stick so the one pad ends up rubbing against the disc all the time. Not enough to slow the car but enough to wear the discs away quicker.
Check that the calipers run over and back freely on the rail, this allows even braking pressure on both sides of the disc, and when you take your foot off the brake, the pads move away from the disc