I can tell you, regular people get tripped up by the simplest things . You thought the button was obvious, but, as anyone who's missed a highway exit learns, in the real world what's obvious to one person who knows the answer is not always obvious to a newcomer . People who are making fun of the voters who made mistakes should think about the obvious mistakes they've made in their lives. I think so. People's confusion, false starts, questions to the person running the test, hesitations, etc., all can point out potential problems even if the actual final performance is without error.
Usability is important in many areas.
Read this letter I received about its role in safety and environmental protection. There are news reports about a simple ballot test with children, but not a real usability test. Includes photograph of ballot in the holder showing the distance and alignment of the arrows with respect to the holes. Complaints about punch card systems and problems with voting machines for shorter people . The design of a system such as a voting machine can bias the results in favor of different constituencies.