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You are correct, turbocharged vehicles should be allowed to run for a couple minutes before being shut down in order to avoid coking. (For those who aren't yet familiar with coking.. basically the oil that sits in a turbochargers oil passage around the bearings essentially "cooks" in place as the turbo cools down.)
On this particular vehicle, the turbo oil return line comes directly off the bottom center of the cartridge. This allows just about all of the oil to drain-back to the oil pan. Since the drain line is only about 3 inches in length, and sits a mere inch above the standing oil in the oil pan it does a great job at draining itself before much coking can occur.
The turbo is the original T25 with 130K miles on it so far. A look inside didn't reveal any crude build-up when I changed the drain line. I don't really cool it down when the turn the car off either. Partially because it's got 130K miles and partially because it's done so well thus far I guess the engineers did a good job setting up the lubrication system.
Engine off coasting / shut downs with out cool down are relatively the same minus the engine turning back on after coasting (usually no more than 2-3 minutes at a time) the oil doesn't seem to get a chance to bake in there as the hot oil resuming flow would push any buildup right out. (this is my theory anyway.)
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