There's another effect beyond cheaper flights.

We moved to the area in a very middle class neighborhood when I was young, around the same time as the author of TFA. Like you said, what I saw was a lot of families had family summer homes on the Cape or one of the NH lakes. Everyone but the Dad would pick up for the summer, and then he'd work during the week & then go to the summer home on the weekend. But these weren't luxury homes by any stretch. These were small, often rustic, closer to shack than nice summer home. A place to sleep at night and not much more.

In the intervening decades, that's all changed. Today's summer homes are so much more different. I've seen a lot of those families I knew back then sell their homes over time. Developers scoop up several properties in a row and build some huge McMansion. So now these areas are the sort of wealthy person summer home people picture when the term is used.