Not just nature, but efficiency. The statement, "In argument subject, not author, holds interest" may be true in theory but in practice this breaks down. People without established expertise may have worthwhile contributions but it's easier for people to receive contributions from people with known expertise. For example, I would just as wholeheartedly receive a comment from cperciva as one from "A well-known cryptographer and talented mathematician with a relevant and competitive PhD."

This is mostly notably seen in the physical sciences wherein most theoretical physics treatises are given little attention from the mainstream physics community unless there is a credible and relevant PhD backing it. Physicists simply don't have the time to pick through all of the papers from amateur hour and point out where they messed up the calculation that they should have learned in Quantum Optics 332.

This expedience is partially reflected in HN comments. While ideally everyone would have a chance to respond to every comment to point out where it is factually incorrect, few have the time. It is also disconcerting to see a factually incorrect comment with more points than the factually correct reply. In each of these cases, one could comment to express agreement with the reply and reinforce the incorrectness of the original comment, but a combination of vote up/vote down fulfills a similar function in a fraction of the time. Perfect? No. Expedient? Yes.