I feel that without knowing these monks' intention, it's difficult to judge this situation. Again, in Thailand from my experience, it's not unusual for monks to be given deference in certain matters. Giving monks a seat in the front of the plane may have been simply to avoid having them in close quarters with women for a long flight. It may have just been a way for the airline staff to make some merit, such as giving monks good almsfood, instead of the dregs. If the monks otherwise refused food after midday, and acted properly within Vinaya rules under the circumstances of being stuck in an airplane for hours, then it's hard to judge them.
On the other hand, if these monks were buying expensive tickets with dana from their temple, eating meals after midday, enjoying the pampering in business class, then it might be said they could leave their robes on the plane, and disembark as lay people.
It all goes to intention and Vinaya observance, IMO. In 2013, it can be difficult for Bhikkhus and Bhikkhunis to be in the world without being seen as being a nonrenunciate. Should Bhikkhus wear handmade, ill fitting shoes? Should they refuse good medical care at a private hospital if it is offered? When traveling to New York for a meeting or retreat, should they sleep in the streets, or can they accept hotel accommodations? If a hotel is offered, must it be the 1 star with bedbugs, or is the 3 star Hilton OK? Again, it all goes to intention.