The estimate that two billion people – just under a third of the world's population – will see tomorrow's Royal Wedding on TV tells us two things. First, it tells us the good news that at least a third of the world's people do actually have access to a television, and indeed electricity. That was not always the case; not many decades ago, abject poverty was the normal state of the vast bulk of humanity. It is the (largely recent) spread of trade and markets across the planet that has changed this.

The second thing it tells us is that people are still interested in the Royal Family. Yes, it is partly the fairytale, the pomp and parades. But we can see all those any time in the productions of Hollywood and Bollywood. There is more to it than that.

The fascination, perhaps, is that the UK – a large and relatively important country – still has a hereditary head of state rather than an elected president. And that this actually seems to work tolerably well (as, arguably, a largely hereditary House of Lords worked).

Public Choice theorists like the Nobel economist James Buchanan tell us that heads of state have their constitutional place. A major point of them is that they somehow represent the whole population, and therefore act as a long-stop against the majority using their political power to exploit the minority. As titular head of the government, the army and the judiciary, the Queen notionally has the power to prevent these institutions being perverted by anti-democratic tyrants. It is not the power that the Queen wields, but the power that she, in theory, denies others. In fact, the present Queen has not done enough to prevent politicians over-expanding their power; but over the centuries, the system has definitely had some positive effect.

The Americans had much the same in mind when they framed their Constitution. Early presidents saw themselves as very much elder statesmen whose role was to temper the decisions of the other branches of government, on behalf of the whole nation. Quite soon, though, presidents became highly partisan, meaning that the power they hold can actually reinforce the excesses of the legislature, rather than restrain them.

As a liberal, I have intellectual problems with hereditary heads of state. But at least they are mostly, in practice, relatively benign. Elected presidents have, by contrast, become highly political and have lost touch with their role as the people's long-stop. It's the elected system that needs the most urgent reform, curiously, not the hereditary system.