I think the relationship is more symbiotic. The technology that enables more remote living includes : better cars, roads, communications, food storage. While none of this probably appealed to your grandfather, it does appeal to today's families. In addition, you can overlay two trends : a trend toward environmentalism and 'enjoying nature' and a trend towards increasing amounts of leisure time. Even the expensive boats you talk about are part of the scenario. Boats that are reliable, easy to use and run, and built primarily for pleasure are a relatively recent invention. Because of the boats, the lakes are more enjoyable, hence more people want to enjoy. They have more time, more money and it's easier for them to do so - and they probably would rather now spend the money on a pleasure boat and holiday cottage than on other forms of consumption, simply because that's the current trend of what you do with spare time and money.
And don't forget that other technological trend : the camera. Ever since a photo could show the beauty of a natural place, the visitors followed. Arguably it was the photos of Yosemite that sparked the initial nationwide interest in visiting such a place. I could theorise that this same trend has worked it's way through into every beautiful piece of wilderness - many people will visit a place simply because they've seen a picture of it. Some of those visitors will choose to stay as residents.
So my theory is that because of the technology and the demographic trends, people populate areas that were once considered remote, and it was increasing awareness of the beauty of remote places that drove the visits in the first place.