Good observation, indeed. The usual Greyhound clientele (the poor and students) tends to be against the war. Last weekend I had a chance of observing a pro-Bush pro-war rally in Harrisburg, PA, en route of that Grehound bus from the story. What I saw was relatively well off older crowd of, judging from appearances, office employees, skilled blue collar workers, firefighter/policemam types, retirees and assorted suburabanites. Some of them were shouting anti-Rendell (newly elected Demorcatic governor) slogans.
I'd say that main supporters are petty bourgeoisie that supported Bush in the first place - they support the war as a part of their continuing support for Bush.
Wojtek