Richard,
While I agree that the NLGs have a harder time finding great sites, I think that they are helped by the fact that golf is now so popular (and there is so much $ in it) that whenever great sites are found they tend to be developed regardless of how remotely situated they are (think Bandon, Sand Hills, Ballyneal, Cape Kidnappers, etc.).
I am guessing that the NLGs face at least two other large obstacles.
1. Technology - I imagine it is hard to design a course that is both fun and challenging for all when the good players are hitting 300 hard drives with balls that do not bend and then throwing darts at the pins with their wedges. I would think that it would be easier to create fun holes for players who you know will be bending and running balata balls into most greens with their 2 irons. Of course, this line of thinking is old hat on this site so I digress.
2. The PGA Tour - TV golf shapes expectations to a great extent and I imagine tends to tie the hands of many good architects. I wonder sometimes how much better Pete Dyes courses would be if the concept of the "championship course" was never born.