my thought on this is that when hoses get old, they get hard. So under vacuum, they would most likely fail if under vacuum (since usually under pressure). If they fail, I would rather them fail while i am in the garage changing the coolant than on the open road.
This is probably what would happen, if it were me...
If I had old and hard hoses, they would find the will and inner strength to hang on during the vacuum fluid change. Holding together just long enough to give me a false sense of security that "they'll be fine".
After I finish my vacuum fluid change and drive around a couple weeks... POW! That's when they will decide to blow out. It would be on the highway, on my way home from work, on a Sunday. Of course, that is when all the parts stores have just closed for the night! Tow home, wait until Monday to be able to get new hoses and lose another day of work at my full-time job to make the repair. Great...
This is probably just how things would play out, if it were me.
If I think of it while doing oil changes, I give a quick look around and give the hoses a good squish to look for cracking and to see how flexible they feel. On a used vehicle, I will eventually replace hoses at least one time during my ownership. I have never actually had hose failure, but maybe this is part of the reason why.
I don't always have the best luck, so I do what I can to be preemptive any time I have the opportunity. I do push things off until summer months, when I can work and not be miserable or frozen solid.