A number of cars do run lean, but the propensity for things to start melting is high, especially on a turbocharged car.

For the original poster, there is a chance that the car had been setup for higher boost ages ago either via the pikey way or with a chip. Even the youngest RST will be knocking on the door of being 20 years old now. With my last car I had these issues to deal with (the car running between 12-13.5:1 on boost with unknown (but no stock) chips amongst other upgrades (intercooler, exhaust etc.) :/).