I think alot of co-worker resentment has more to do with the way company travel is decided and allocated by management. Obviously some jobs require travel, and others are just enhanced by travel. Or certain trips are approved for "good will" reasons, while other similar trips are denied because there is only so much money in the travel budget for "non-essential" business travel.

Last year, a domestic trip I was "promised" by my supervisor and which was approved in the travel budget was "taken away" from me so a co-worker in my department could take an international trip, which was not originally budgeted. When I voiced my objection, the response I got was "You don't really have time to take this trip." The implication was that my co-worker "got" the trip because he had less work. Both trips were "goodwill" client visits. I was extremely resentful of my co-worker, not because he got the trip, but because my supervisor chose to "reward bad behavior" (i.e. the person with less of a job) instead of "rewarding good behavior" (the person who works her butt off on weekends and holidays because she has too much work and not enough help). However, I am mature and professional enough to realize that my co-worker was not to blame for his "good fortune."