People stake their Bitcoin address and message because they need other forum members to quote that message, and verify it. The most important is quoting it because if no member quote it, if a Bitcointalk account is compromised, hacker can delete that post.
Quoting it helps to make it easier when it needs to be referenced, but with the forum scrapers we have now that log all posts made, the original posts with the address can always be pulled up if the need arises.
For older posts that were made before forum members started keeping logs, quoting is the only way to preserve them.