Definitely true to some extent. I think the degree to which it applies corresponds to how deeply a person engages with an individual post/thread. Having long conversations in the comments of a post is probably not conductive to shortening attention spans. Ideally we could mimic the sorts of deep conversations that can be had with small groups of people/friends in-person. Maybe Hacker News would benefit from live updating comment threads so that people wouldn't have to refresh the page frequently to have a back-and-forth conversation.