Someone provided a very nice calculation of the number of potential photographic art collectors about a decade before I ran a similar calculation. The difference between my calculation and this author is that I assumed all art and came up with a figure of a most 300,000 potential buyers in the USA. The author's calculation of 10,000 collectors of photographic art seems about right.
Without going into details, I feel the collector market for photography is indeed rather small. With a large number of artists vying for print sales, it puts pressure on photographers who work in the area of collectible photography.
No matter how you view it or what you believe, its important to understand the forces in play.