Is the {forum} table redundant?

From the Drupal 6 release announcement:

Forum improvements
Include polls, quiz forms or any other type of content in forums.

I understand this to mean that any node (of any content type that supports the Forum vocabulary) that has a term of the Forum vocabulary assigned, is in that forum.

IOW, any {term_node} record with a tid out of the Forum vocabulary would also be in the {forum} table.

Am I missing something?

I've created an event (not forum topic) and assigned a forum term, and the event shows up in the forum.

How would you assign a forum term without having the node show up in the forum?

There's a query in forum_get_topics() that goes like this:

SELECT n.nid, r.tid, n.title, n.type, n.sticky, u.name, u.uid, n.created AS timestamp, n.comment AS comment_mode, l.last_comment_timestamp, IF(l.last_comment_uid != 0, cu.name, l.last_comment_name) AS last_comment_name, l.last_comment_uid, l.comment_count AS num_comments, f.tid AS forum_tid 
  FROM {node_comment_statistics} l 
    INNER JOIN {node} n ON n.nid = l.nid 
    INNER JOIN {users} cu ON l.last_comment_uid = cu.uid 
    INNER JOIN {term_node} r ON n.vid = r.vid 
    INNER JOIN {users} u ON n.uid = u.uid 
    INNER JOIN {forum} f ON n.vid = f.vid 
  WHERE n.status = 1 AND r.tid = %d

If n.vid = r.vid = f.vid, shouldn't f.tid be the same as r.tid? Why join with the {forum} table?

I got my answer: {forum} has only one (nid/vid/tid) record per vid, namely the one referring to THE forum which contains the node. If a forum topic is moved from tid1 to tid2 and the user chooses to leave a shadow copy behind, then {forum} will have (nid/vid/tid2), and {term_node} will have both (nid/vid/tid1) and (nid/vid/tid2).

In the query above the JOIN with {term_node} and the r.tid = %d condition gives us not just the nodes in %d but also those that have shadows in %d, and the JOIN with {forum} gives us f.tid AS forum_tid, so we know whether we have a forum post or just a shadow.