To take a recent example from a country that shall remain nameless, how do you stop a magalomaniac from duping half the population with a mix of nationalist rhetoric and promises of rolling back any half-uncomfortable environmental or sociological progress? If the whole government gets tainted at the same time, even if the country realises its mistake half a decade later, the money wasted in switching the laws back - the economic equality and environmental progress lost, the damage to international relations... all because the person in charge doesn't actually care about the country, and there is no ironclad process for getting them out of power (besides the collective power of a government that is either scared of his voter influence, or realises their power is contingent on his)
None of the laws this article claims the Queen has "influenced" worry me in the slightest. It doesn't benefit anyone to know how much wealth she has (in fact, if something should happen and her wealth fluctuates drastically, that could cause more damage to public and international perception than good) and the law has always maintained, as far as I'm aware, that many driving laws do not apply on private property - Sandringham et al being considered private property for the purposes of this law makes logical sense to me. The national monuments one is just bizarre, smacks of a power-grab by government - albeit a petty one. I suspect it was a way of getting more tourist revenue. But either way, its not exactly earth shattering.
"But what if Prince William becomes king and uses these powers for evil purposes?" I hear you cry. Well, in that case something will change. Either an uprising will happen or evil will be done. Though as long the monarchy's well-being for their whole life is entwined with the country's well-being, there is less likelihood that a sane king or queen would rock the boat significantly.
I seriously doubt that this is the law that will cause the next major catastrophe. As that certain other country has proven, unbridled democracy is a more potent threat.