> And by “topic”, in the case of HN, I mean the title of an article.

The thing is, the topic of the actual article is generally more interesting than the topic suggested by a naive reading of the title (as is the case here).

People discussing things based on titles leads to generic discussions that recur again and again and go nowhere. Whereas the actual topic of the article's content is rather more specific and could lead to an actual new and more specific discussion that might actually go somewhere.