Tom,
I told this story before, but the Chicago phone book had several golf ads circa 1960 which touted "elevated greens" as a design feature, which 15 year old me took as a clue that their course was "professionally designed" as opposed to a mom and pop type deal, so I agree that RTJ and his style probably influenced a lot of people to build greens up. Just a guess.
Of course, Chicago, with its clay soils and occaiasional springs, made it "safer" to build things up. I recall a Dick Nugent maxim was that the front of the green should be no less than 1.5 feet above the front grade, because it just didn't seem right to cut a green in when filling with USGA sand.
Killian and Nugent also built the fw bunekrs above grade, but mostly because they were more visible.
Greg,
Think what you want, but the cut and fill has to balance, and no one wants to haul dirt very far, either. Once you generate the 30-45K dirt out of the required irrigation pond, it has to go somewhere. If you look closely, you may notice more work near ponds, either higher greens or tees, or more fw features.