I've occasionally had rental companies limit me to nearby states, but they usually don't care. When they do care, I'm certain they can be made to stop caring if you apply enough money to it.
Rental cars (booked in Germany or Switzerland) often included restrictions for me.
Most of the time they excluded a number of eastern/balkan states, quoting (if they offered reasons at all) insurance prices would be higher. The more expensive the car, the more likely were these limitations: Booking a Golf was 'go anywhere', booking a BMW 5-something .. not so much.
Completely irrelevant. We aren't talking about Germany or driving to other countries, that's totally different. We are talking about travel within one's own country. I would expect rental car companies to limit travel to foreign countries.
We = this article and the commenters on this article. We are commenting on travel between two US states, nothing to do with crossing country lines. The grandparent topic was, specifically, about ground transportion for four Americans from one part of the US to another part of the US.
Well, this whole subthread is about an American airline operating in the US. (And yes, you can potentially drive a car across an international border from the US!)