After consultation, the consensus is that it will remain as is. You can delete your own posts, but not your own topics. This is to avoid one user deleting another's post in reply to a topic (which they may have put some effort into).
If you wish a topic to be deleted just PM a moderator or admin, or just retitle it "*** Please Delete***" or something to that effect.
It occurs to me that a permission to the effect of "Delete own topic with no replies" might be nice, but such a permission does not exist in SMF 1.0.5.