What about new members who want to have something to say on a topic that has attracted their attention, only to find the thread they've contributed to has been locked in the next posting.
Surely if a thread has naturally "died" once from lack of interest, who's to say it won't just die again, there shoudn't be any need for this sort of euthanasia...
This is the only forum I know of where threads are deliberately locked simply because of age.