That is more like deleting a post.. tried testing, you can't delete a topic but you can delete other posts and i think the only reason an author will edit a topic to "." Is because he can't delete it , so it's probably going to report it or still get reported anyways but it's still not bad to have it because with the report option it get recorded as " deleted by moderator" .
As users, it's only allowed to delete posts, and not allowed to delete threads. Only forum moderators, admins can delete threads.
If your post is spam, and reported to forum staff, it will be deleted if forum staff agrees with a report against your spam post.
If your post is in a spam thread, and that thread is reported to forum staff, and the staff agrees with a report, he will trash that thead including your post.
An example is Ratimov, with many self-moderated threads. He deleted many posts of forum members in such self-moderated threads, but when he wanted to delete his threads, he reported it to moderators. Some threads were deleted, and some were not, it's up to moderators.