Mark,
I think the more interesting question to me is: How many of the courses that started on DS 2 or 3 sites, basically remained that once the course was put in the ground? Sure 7 or better sites are always great, and in raw numbers, I would think that only reflects a very small % of the total courses built.
But for the tens of thousands of DS 1-3 courses, that effectively serve the golfing masses, couldn't more have been done, even on a limited budget to turn a DS 2 site into a DS 4 or 5 course on a more frequent basis? As one who has played most of my golf on public courses, it seems like most were just putting another course in the ground in turn-key fashion, instead of getting the most out of it.
If attempting to evaluate the body of work of an architect, I would probably look more favorably on one who took DS 1 or 2 sites and consistently got 4 or 5's out them...over one who primarily worked on 4 or 5 sites, and turned out 5s and 6s.