most of the members will be reluctant to answer to those threads after being warned not to post anything on such threads.so it is better to delete it together.
I think admin have other important and valid jobs to perform therefore they are taking it as secondary to delete the no replies thread. May be the no replies thread is kept because the admin hopes that it might well be answered by us and they are quite valid posts...!
Many posts give good information but do not need reply. It makes no sense just to write- very nice information. Ifthe topic is not controversial or debatable and everyone will just agree, there would be no response. Hence 'no replies'.