It's odd! The guidelines don't say anything about having to read or watch what the posts linked to, all they say is it's inappropriate to accuse someone you're responding to of not having done so.

There is a community expectation that people will know what they're talking about before posting, and in most cases that means having read the article. At the same time, I suspect that in many cases a lot of people commenting have not actually read the thing they're nominally commenting on, and they get away with it because the people upvoting them haven't either.

However, I think it's a good idea to do so, at least to make a top-level comment on an article. If you're just responding to someone else's comment, I don't think it's as necessary. But to stand up and make a statement about something you know nothing about seems buffoonish and would not, in general, elevate the level of discussion.