When I set up the forums, I had set this forum and the graveyard to only show topics from the last 30 days by default. Of course you can override the filter -- at the bottom of the topic listing page for any forum you can specify to show only topics from a certain period or all topics. My intention was that only recent posts would be of interest in certain forums, but I can see now that it's slightly confusing.
So it has now been changed -- all forums now default to show all topics, period. Except one - the bug reports forum, which defaults to show all OPEN topics, meaning topics that have been locked will not show up by default (because I lock the topics in that forum when I fix the bugs so it's easy to keep track of which issues have already been addressed and which are pending). And of course you can override the filter at any time so if you wanted to look back through old bug reports that have already been addressed you can do that.
Eventually if the traffic on the forum gets big enough that its worth it to start limiting what shows up by default it might be changed again, but for now I think showing all topics on all forums is probably the way to go. Thanks for bringing this up so I had a chance to reconsider my initial choices, I think it's probably much better this way (for now anyway)