At the U.S. companies where I have worked, Microsoft Office is so heavily used that Windows is the natural OS choice. I don't see why the computers in airports used for ticketing and flight information should be running Windows, though, even if it makes sense to use it at Delta corporate HQ.
No one ever got fired for choosing Microsoft. What other platforms offer enterprise support for airline-sized corporations?
Is something like Red Hat Enterprise Linux not suitable? I'm not saying that staff at HQ should be forced to use it, but I think RHEL terminals would make more sense for ticket agents, who aren't making PowerPoints.