HN has a convention of using the headline from the article, and it puts the article's publisher name/domain right after the headline, like attribution. So the impression is that particular publisher is saying that thing definitively.

The difference of "allegedly" is big to a publisher (missing it can break their own company), and to a journalist.

Because of this, I think it's also a big difference to the savvy reader. When an outlet dispenses with the "allegedly" or phrasing as someone else's claim/assertion, that feels to me like a rare occasion on which they really want to impress that it's definitive. And that they know what they're doing, and that experienced readers can tell. Never crying wolf. (A little like how you'd say "literally" once in a decade or lifetime, with emphasis, for impact, when it was really true.)