Many of them are not. If the problem is with the rim it will be at the same spot. If you mount the tire with brand name over the vent and there is a problem with the tire than you have not identified and fixed, it will be the same spot again. On another angle, even those cases with embedded shards of glass or thorns are most often progressing events where the puncture could be stopped if the tire were examined soon enough. There was a period when tire wipers were used.
I agree with you. I use to live in the Mojave Desert of California where goat head thorns were all over the roads. When I first moved there I averaged a flat a day sometimes 2 flats in a day, they were indeed quite random where they would enter a tire. So if they're getting a flat in the exact same spot then there is something else going on that isn't random like a thorn would create, more than likely there is a tiny bit of a thorn still sticking through the tire that the poster never found.