i'm not saying this one is... i know some of the moderators here feel as you do or have had similar experiences.
i'm just questioning the status quo i guess. just because everyone does it doesn't mean it right.
mini-zracer is a VERY active forum and the policy i've encouraged has worked very well for us.
for example, i don;t know that many of the other well respected mini-z forums that have similar policy's torward old threads. i find that policy most often occurs in forums that have a significant number of very young members, like dedicated xmods forums and forums with very strict rules and enforcement.
take a look around r7r which has a VAST collection of some of the best project threads, that get bumped from time to time as things progress, new things make the same project easier, etc. i often see this on bitpimps as well.
every forum has it's own flavor and feel to it though.