No surprise on the motivation for this thread.. The closed thread is on the 2nd page, not that difficult to find. I think another thread was merged with it (the link in the OP), and the soft link drops off after a set period of time.
Erm, it might've on page 2 here. But those following a link from another site or had the page bookmarked couldn't directly access it.
If what you say about soft links is true then the link would be in place for days if not weeks, rather than just a few hours!
I've encountered many merged threads before but never any broken links.