The US isn't a democracy. It's a republic. EDIT: The "it's a republic" comment was meant to point out my superior intellect and immense knowledge of all political issues. If any of you ever need any advice on who to elect as the next PotUS, just message me. Spoiler: You need to vote for Ron Paul. Damn those who think the government should have control over healthcare, we're not Canada. We need to keep our ideals separate. This is all just some master plan to merge the US and Canada into a super-country that will rule North America. People will then rebel in retaliation to the merger, and a violent war will be waged from either side of the border. Hockey pucks will be found lodged into Americans' skulls; there will be a note left in the victims' breast pocket reading "I'm sorry." Canadians will be found lying on the side of the road, dying. Cholesterol overdose from the invasion of American fast food. No apology. This is war.
If you're talking about that study, there are some serious methodological problems with it. First an foremost, it simply assumes that because government actions are more likely to align with the interests of the wealthy than those of the larger population, the wealthy must wield the power, while, as they say in the study, it is largely accounted for by the massive status quo bias of a bicameral legislature and the other checks and balances of the federal government.