Remember folks, it's all about suspension of disbelief. I think this alternative, and the fact that (as I recall) Tolkien didn't address it has more to do with how common (and cheap) commercial air travel has become than it is about Tolkien not talking about something obvious. Keep in mind Tolkien grew up during a time when walking really was the most common way of getting to and from places, and air travel was simply unheard of.

Doesn't stop us from making fun though.

Via Yourish.