Whilst I agree that the programme was somewhat misleading, some of it was actually fairly true to life in my opinion.
I have actually been to Vava'u the main island where Kevin was picked up from the dock, and it does take for-bloody-ever to get there! Go to NZ, get on another plane for four hours past NZ, get on another plane for a couple of hours and then by road to the dock.
Whilst they would have to buy some food in, a veg garden is a necessity, as the market on the main island has whatever the locals have grown and you can never guarantee what will be available. The actual shops for stuff like beer are about the size of your average one corner shop and are full of very random items... From memory there are no shops on the other islands in the chain, everyone has to come back to Vava'u, and if the weather is too bad to use a boat you're stuck until it is. And if the weather is too bad for the supply ship, tinned food gets very boring!
There are a few other expats around and they tend to get together to socialise when they can, and quite a few have kids of a similar age, with most going to boarding school when they reach their teens. You also get lots (in relative terms) of visitors coming in by yacht and staying a while.
All that said, you wouldn't catch me living there in a million years, whilst a two week visit to stay with friends was an amazing experience, it is way to remote and incestuous (the mad expats - not the locals) out there for me.
Oh and in terms of building using what was on the island - I've never seen rebar (iron mesh for reinforcing concrete) growing in the wild!