Sorry, but I have to reject the "one horse, two acre" rule out of hand for anyplace I've ever lived and kept or boarded horses. Now I've not lived everywhere, so maybe in some places it would be a norm. But somebody is going to have to give me some of the 5Ws on why it's two acres, as opposed to 1.75 or 2.25.
THis is going totally off this thread
In the UK (where I come from) its basic guideline given out by the British Horse Society and is just that - a guideline. Its based on average horse in average work on average ground - do you get what I mean? It wouldn't apply to desert or woodland but grazing land only in a climate thats moderate. Its based around that being the only land you have - no extra acreage to rotate them around. Its supposed to allow sufficient grazing for average summer months with enough space for horses to move around freely and for the land not to become sour - daily muck removal is part of the BHS recomendation.
If you manage your horses differently - more stabling, more riding work, more land for rotation and you have more extremes of weather and ground conditions as we do in parts of the US or other parts of the world then surely its common sense that you will go by different rules
I will say though that I like my horses to be able to go into the field and have a good run around if they want too and not be stuck on some patch thats barely any bigger than a stable
If you and your horses are happy then why would you worry about rules or what anyone else does. I dont.