My commute is 35km/22mi each way, 4 days per week. I have the option of doing a multi-modal bike/train commute which cuts the biking portion down to 15km/9mi each way, but I prefer to ride when I can because the train is often crowded and sometimes on strike. However, I work at a desk all day, so my commute is my "outside time". If I worked long days outside, I would find it much harder to have the energy to put in those 3hr round trip commutes. Also, if you don't have to deal with traffic or toll/parking fees, it'll take a lot of willpower (or incredible scenery) to pull over before your job site and bike in the rest of the way.

There is another BF member (CCrew) who used to have a 74 mile commute each way. He drove 50 and biked the other 24. In his case, the last 24 miles had terrible traffic and expensive tolls.