I've noticed the same trend, and have similar concerns. It's not that a clarification or correction isn't necessarily a high-content comment, but it's far from guaranteed to be the highest.
I think the "minor gripe" is actually HN's version of the meme reply: easily digestible, doesn't take much effort, and easy to agree with. Just as reddit's frontpage is dominated by imgur links, so too are the comments on HN dominated by easy criticisms.
I've said this before: for any given story there will be people who disagree with it, and the way HN is currently designed, upvoting a critical post is their only way to express that disagreement.
I think the "minor gripe" is actually HN's version of the meme reply: easily digestible, doesn't take much effort, and easy to agree with. Just as reddit's frontpage is dominated by imgur links, so too are the comments on HN dominated by easy criticisms.