Patrick,
Wild Horse is hardly a cornfield and if it ever was one, certainly not the best of cornfields. From what it sounds like, Andy is not referring to the type of topography that Wild Horse presents. While I wouldn't compare walking Wild Horse to climbing a mountain, it's got plenty of elevation change to keep things interesting.
Also, if it can be considered a part of the "land" for the course, the wind obvoiusly allows for plenty of variety in playing conditions. I don't think it applies as a "flat cornfield".
Finally, I don't see how a better site does not yield a better golf course, all else being equal. If you give the same architect the same budget, timeframe, construction company, etc. with one site in the sandhills of Nebraska and another in the flatlands of Florida, it seems pretty obvious that the better piece of land would allow for a better course.
That being said, I think it's also fairly obvious that with nothing being held equal, except the architect, it's possible that the same guy will come up with a better course, but the better site would produce a better course more times than not.