There are good reasons to do that, e.g. to be a one stop destination for news on a topic, but from aggregators like this it's preferable to link to the original source because errors are less likely to have been introduced by broken telephone, and to give credit where credit is due.
Though I would still argue that by definition, sites like Hacker News are also aggregators in the same way, so I think it's slightly disingenuous to pick on one and not the other.
IME, HN posts aren't ever a source of the content linked, only as a source of comments. Plus, HN doesn't run ads on its posts.
Lastly, evbite the-site-itself appears currently not to be...up.
Blogspam isn't a judgement that says you shouldn't read the article if you're on the blog (or read hn), it's a judgement that you shouldn't link to it on a news aggregator, or generally use it as a source.