Nordic skiing is more similar to cycling and rowing, in that the fatigue is a different kind of fatigue compared with running a 5000 track race, which is intense and produces quite a lot of trauma on the legs and body.
Cross country skiers can race a 15km race, and they will feel tired, but they will recover and then be in shape to ski another race a day or two later....in running it does not work like that - the trauma to the legs is much more devastating.....
So, again, we are talking about different kinds of fatigue.
Nordic skiing, cycling and rowing tax the muscles in the body more than running, and of course, there is little trauma to the body with nordic skiing.....at the end of a race, nordic skiers will push the envelope and go into the 'anaerobic zone' but most of the race is in the 'aerobic zone' which they have developed thanks to training 4-5 hours a day.....which you cannot do with running.
In the 50km 'freestyle' cross country ski even at the recent Torino Winter Olympics, it was interesting to note, that right up till the end, there were around 20 athletes in close contention.....and it was very aerobic, in that these athletes were capable of talking to the coaches on the sides during the event.
Ask a cross country skier how he feels after a race on skis, and he will admit that the recovery is much faster and better after cross country skiing, compared with running, which is a much more destructive sport because of the constant trauma induced by limited repetitive movements on selected body parts....