There ARE some legitimate reasons to reply to an old thread though, so we can't make it impossible, although the significant majority of necroposts are not generally beneficial to the thread.
here is a good example of why sometimes a thread needs to be updated
This was not a VERY old thread ,but the program in question has gone through some very significant changes
qt3 and gtk2 gui to a QT4 gui
and a search here , for the program,pops up the post .