The intercooler have nothing to do with this.
The main reason behing letting the engine idle for at least 1 minute on a turbo car after a hard run is the turbo's turbine shaft bearing. If u switch off the engine straight after a hard run, the heat within the turbo will burn off the oil within the shaft assembly as the oil have stopped circulating. By letting the engine idle for a while would've let the turbo cool down, as it's not producing any boost as well as the circulating oil would've taken heat away from shaft bearing.
Unless the oil circuit is designed to continue circulating after switching off the engine, it is still beneficial for the engine to idle a bit before switching off, or u can just drive slowly before parking the car.