I would argue that any system inherently decays into an oligarchy, hence 'democracy' is something of a relative term. Rich people, charismatic people and ideologically popular people will always have more power than poor, unremarkable and isolated ones. This is true under monarchy just as it is under democracy. What matters, I suppose, is widening the oligarchy, and controlling it. It's far less objectionable to have a system in which those most able to persuade people have more power than it is to have one in which those who own the most land control politics. Even that, though, is hardly perfect: as the Athenian democracy ably demonstrated, persuasion is as much a factor of education and preparation time as it is a matter of natural talent or even - God forbid - soundness of argument. Any citizen man could speak in the Assembly, and yet every one of Athens' influential 'politicians', inasmuch as we can apply that term, was an aristocrat. Demosthenes allegedly locked himself away for two months on end to practice rhetoric: this was far beyond the means of anybody who had to actually earn a living.
There's also a question of limiting the severity of the oligarchy. It's worse to have a situation in which 75% of the people have power and 25% are ignored totally than it is to have one in which 60% of the people have slightly more power than the other 40%. The former situation, of course, often ends in a mess. In 1861, Abraham Lincoln was elected despite not having appeared on the ballot paper in most Southern states. Knowing that they no longer had meaningful influence in national politics, and fearing that the majority would be able to enforce its will on them, the South seceded. This would perhaps not have happened under a system with no presidency and a more (an even more?) limited government.