You're off to a good start, there. I like their reasoning and I think it's going to lead to some interesting consequences, even if Peter remains the secret keeper, as Dumbledore -can't- have near as much influence in the US as he does in England and that'll change a number of things.
I'll agree with jabarber69 about the area around El Paso, TX being an equally isolated place and I do think a Harry Potter raised in Texas and picking up the attitudes around here (Can you tell I'm a Texan? Not by birth, but by upbringing and later by choice) would do wonders for shaking up Hogwarts - there's a certain irreverence toward authority and distrust of government in the culture here. Still, the area you mentioned is still in Middle America and likely would have many of the same Jeffersonian aspects to its culture. I don't know enough about the other schools to know that Hogwarts is the best, but I admit I do have to wonder given some of the teachers seen in canon and some of Dumbledore's choices, unless, of course, one goes for the Manipulative!Dumbledore or worse viewpoints.
I can't help but wonder if the wizarding education in the Americas would start earlier than in England, America likely being a lot less tradition-bound, and Harry would go to Hogwarts rather more skilled than he was in canon.
Author's response
The attitudes are present here, along with a strong influence of 19th century German immigrants. The southern attitudes are tempered by the fact that it is farther north.