It might seem to make sense for the editors to merge news threads with user-started threads because it's nice to have all comments in one place, but in practice it's usually a disservice to other users.
Sometimes it's not practical, such as when there are different conversations already going on in the two threads (so they wouldn't make sense merged), the user-started thread has gone off topic or doesn't cover exactly the same news item, or the editor doesn't know about similar forum threads. It also breaks users' thread subscriptions and bookmarks for the thread that is merged away.
More importantly and more often, the news story will include details, links, and often a photo or graphic (as is the case here), making a better presentation of the news for those who haven't already heard about it. When threads are merged it's chronological post by post, so the news story might not even end up on the first page of the thread. Often a user posts a quick link yet an editor actually knew about the story sooner and is researching it and writing it up. And moderation is stricter in news threads so a user-started thread, depending on the forum, may have posts that were fine in that thread but would be too much clutter in a news thread. For these types of reasons it's better to credit a user who submitted a news story than to merge the news thread with a thread started by another user.
It's easy to second guess when you're not the one making the call, but it's an issue we've considered and talked about. We used to merge news threads with other forum threads routinely, and it caused problems regularly.
MacRumors has no reason to cheat users out of credit. Quite the contrary. Everyone wins when we encourage people to submit news and rumors by rewarding whoever is the first to provide a tip.
If you want to discuss news thread merges further, please start a separate Feedback thread. Thanks.
