That's fine as long as if you just did a drag race. If you watch exhaust gas temperatures after a hard run, they cool down within seconds and the exhaust can cool down within a minute or so. It's cast iron so it does hold some heat but that's why you should use synthetic oil on turbo cars anyways.
During normal driving, these components don't get too hot (relatively speaking) and can cool down as much as they're going to cool down in under 10 seconds. If you're pulling off the highway, the coasting down while decelerating is enough. After all, who is going 60 mph and then shuts the engine off immediately? If you're getting off the highway, you slow down, end at a stop sign, or pull into a parking spot. If you're driving locally, it's not going to get much cooler.