Patrick,
Although it's certainly desirable, I don't think it's mandatory, unless you're talking about dead-flat ground.
As in real estate, I think it all comes down to three things..."location, location, location". I can think of numerous green sites in the Philly area, not built on natural sand (including some we saw at Inniscrone, as well as a number at Stonewall), that just flow from the fairway completely naturally without being built up on high fill pads.
Although I'm hardly an expert, it seems all you need is a slope to built into, and let the natural drainage happen in whatever manner that slope falls. Just like Garden City, isn't it fun when a green drains to one side or the other, or even more thrilling, to the side and back?
Any architects out there care to weigh in?