The upper echelon of society, on both sides of the WBTS, not only did their duty, but (for many reasons, not all of them noble) were usually the first to enlist. It's such a shame that so much of that good DNA got permanently filtered out of the gene pool. We sure could use it now!
As far as noblesse oblige is concerned, you see vestiges of it these days, but it's only a phantom of what it used to be, at least on the upper end of society as far as I can tell. Maybe when everything became "all about me," it evaporated at that level. But you still see it, primarily in the everyday rank and file American, who, if they were to try to put it into words, might simply refer to it as "giving something back." They are the true appreciators, in my view. God bless 'em, we'd be even more screwed than we are now without them.