Have you talked to veterans or families of serving soldiers recently? Judging by my canvassing, plenty of them speak that way as well. My last sting was right next to a huge military base (Fort Belvoir) and not so far from the Pentagon.  Mainly not affluent - in fact that seems to be rather rare.

 While I agree with you on who joins up, I think they are a somewhat self-selected group from the poor and middle income population. Most wouldn't have joined if they didn't see it as a way out of a dead end life, but the patriotism stuff tends to be a secondary reason, indeed it's what distinguishes them from their peers who don't enlist.