Actually, for the most part, it is all about commuters. US has been around for so much longer. During that time, the company has closed multiple bases in multiple cities. Particuarly the west coast. Those people are some of the most senior so, since all the pay cuts, they fly international. International flying makes it nearly impossible to list for the FCFS system within the 12 hour window on the return of a trip from Europe. While I am not advocating for either system (especially since I am on the bottom of the seniority list) I can understand that there are just somethings you earn over time. Non rev based upon seniority is one of them.