Fluoridex and other OTC, high-fluoride toothpastes

I've noticed that several non-prescription toothpaste brands with 1.1% fluoride can be found online. I've also seen a few "dental supply" websites that will sell Clinpro and Prevident -- or what they claim are those brands (at $35/tube) -- without requiring a prescription. Why is that? Is "prescription only" a legal requirement, or is it more of a gentlemen's agreement (for lack of a better term) between the ADA and the makers of the top brands?

Note: I don't have an ax to grind; I'm just genuinely curious. (I used to think prescription pet foods were just a marketing angle, but now that I have a 20yo cat in delicate health, I know better.) With these toothpastes, I've read there's a risk of small children eating the stuff like and getting really sick, and of course the risk of white spots on developing teeth. So I can't help wondering what the story is.