Regarding this question, you should have asked maverick. We all know that there is no delete option for polls as well as articles once if we post. similar to that there is no delete option provided for q and a too. As rajnini said there are some security issues and to avoid spams.
In Questions and Answers section there is no delete option and i think due to security reasons they havent introduce. There is no edit option too so you cannot delete or modify them. These option have be introduced yet.