Padraig:
Elevated greens are a function of building courses on poor soils, where it's more efficient to bring in fill for the greens than to try and screen the soil sufficiently. So, you don't find them on the heathland courses much, but you find them on other golden age courses such as Winged Foot.
However, some good-player architects also rationalized elevated greens on the belief that they "reward a good shot", by penalizing everyone who misses the green -- so they multiplied beyond their functional rationale.
Trent Jones certainly did not invent elevated greens, but by trying to set a style of his own that could be adapted to any site worldwide, it was a logical choice.