I know you don't need a boat, but it would certainly help. I wouldn't want to rely on someone else to get me on and off the island, especially in an emergency. Even if you don't own a boat, you still need to keep a dock in working condition. Oh, and if you do have a boat, that's another thing to maintain. And a boat isn't going to get you to the grocery store (unless there's a canal. Or an inlet. Or a fjord).

I keep thinking about things like maintenance. If you need a new roof, you've got to find a roofer willing to load up a boat full of shingles, ladders and a roofing crew. That's going to increase the cost.

And then there's insurance. I imagine that standard homeowners insurance isn't going to cover you quite like it would elsewhere.

I have a friend who lives in a house near a mountain top, in the middle of a forest. There is a road leading to it, but you need a good 4x4 car to get there(no, a BMW X6 or Audi Q7 will not get there without destroying the underbody), and between November-March you can't drive at all due to snow - to get anything up the mountain they actually use a horse-drawn sled(and the horse if nearly drowning in snow anyway).

And you know what? He has electricity,and internet, and fresh water. He managed to convince the utility company to lie down cables all the way to his house, and uses a well for water. He has house insurance. As for roof/maintenance problems - he just brings the workers up in his own car during the summer. He even gets post(in the summer, but the postman is a seasoned hiker) and has an actual address.

Compared to this, I think owning a boat is actually less trouble.