IMHO, the whole discussion is pointless if "unreachable by miles" means you have to go "the last mile" using miles (pardon the pun). People often don't fly to the country they're going to visit if it's cheaper (or better miles availability) to fly to an adjacent country and then take some form of ground transportation the rest of the way. For most people traveling internationally, the important thing is to the "big" part of the journey on miles, not every single part of the journey on miles.

So that's why I think your focus on "you can't get the bus from FCO to Vatican City with miles" is ridiculous. Because it implies that I can't visit Vatican City with miles the same way I can visit Italy (beyond the aiprort hotels) with miles, and that's ridiculous.

A couple years ago, I flew into Switzerland to visit Austria, because ZRH had better miles availability. And on that same trip I visited Liechtenstein, which has no airport of its own. As far as I'm concerned, I flew that whole trip on miles, as so I visited Liechtenstein with miles, even though I didn't fly into Liechtenstein and couldn't have. The trip across the pond was on miles, and that's all that mattered.

It would a horrible value to redeem miles for a local bus, if you could. It's typically a horrible value to redeem miles for a rental car, but you may be able to, by why would you just to say you were able to get "the whole trip" with miles? It's silly. You use miles to save money where the money would be costly; you don't use (many) miles to save (a little) money, that's a total waste of miles.

This thread exists because there are countries that are unreachable on miles even if you want to drive a few hours or take a train without using miles. They're not so much countries without airports as countries with airports only served by small local airlines which do not participate in any mileage program. It's not a thread about "countries without commercial airports within their borders", that would be a different thread.