Old feature or what?

In that bumped thread from 2004, this one, at the bottom it says similar threads but not on threads now?

whats that all about alfie?

Yeah, I noticed that a while ago when i bumped another one.

Yeah it's on all the old threads.

I cant actually think of a logical explainable answer for why that would occur for those threads yet not new threads. Respectively they should appear for all threads or no threads as it isnt something that is stored when the thread is created.