Coming from a family of Truckers and Diesel Mechanics, I was told the same thing when I bought my first diesel pickup, with a 6.9. I did my best to avoid short trips and would idle, whenever practical, mostly in cold weather. I did the same thing when I owned a non-turbo 7.3. Other than an injector pump going out on both motors, and having to replace a few glow plugs in the 7.3, in the dead of winter, of course, those motors were bulletproof.
I used 10W30 in the dead of winter in both,15W40 the rest of the year. I noticed easier cold weather starting on those motors, too.