I'm pretty sure that this used to be true on earlier turbos without intercoolers and even then it was only after the car was run hard. Modern cars with intercooled turbos don't need to be run for any time after stopping. If run hard, you would here my Audi's intercooler run by itself a few minutes after I shut it off. If you were really beating on it, you can run it for a minute or so just to be safe but I have never heard it to be necessary in modern turbos.
2012 328i Base, Auto, Melbourne Red