Also, if you go for long periods of not paying any "national insurance" (similar to social security) you can actually not receive the govenment pension on retirement.
Still, having the major stress removed of worrying about healthcare is reason enough to enjoy living in the UK over the US.
It is in Scotland.
(I'm not 100% sure how this is enforced. It rather seems as though getting a cheap flat north of the border and declaring that as your normal residence for the duration of studies could be worthwhile if you can afford it...)
It's debatable whether it's very ethical to do what you suggested - though I don't imagine it's particularly common.
The university would presumably also expect a Scotland-resident student to take Scottish exams at a Scottish school, which is a separate system to England, so even more hassle.
Besides, even on Scoraig, people are paying tax, and probably at a high proportion of their small income. Everything bought from the mainland will charge VAT; fuel, alcohol and cigarettes brought to the island pay high duties; and I have no reason to believe they're not paying council tax either.