Last modified: 2011-03-26 10:05:13 UTC
Since single contributions to threads can be editd, they should have an edit history tab with all the usual (list, diffs, permalinks, etc.)
It's not a tab, but it exists. Look under the "Options" drop-down. I'm not interested in bugs asking for it to be moved, because the interface is being redesigned anyway (see the LiquidThreads extension page for full details)