This is my least favorite ECCIE rule.
It is too binary.
People should be able to exercise common sense and bump a thread that may have been dormant in excess of 30 days as long as the bump relies on the relevancy of the previous posts within the thread.
Starting a new thread isn't a good approach in some cases because the brain trust in the original thread is lost as it rolls off.
I prefer common sense to hard and fast rules whenever possible.