The admin has to delete accounts if it is done any other way than a ban - and he is a very busy person.
I would be surprised if an "off topic" thread of this type would catch his attention - so a request such as this could easily go unanswered.
All the mods can ban people which produces the same result - no more postings can be made using that account.
If anyone wants their account deleted by the admin they should click on the "contact us" button at the bottom of every page.
They can thus send a message directly to the admin.
He will then deal with it when he gets the chance...
Very few people ever request that their account is deleted (the vast majority of the people that get banned have broken the rules - this is well over 99% of the bans) so it has minimal effect on the available pool of usernames. I am not sure whether the username could be reused after an account deletion that the admin does - that would depend on the intricacies of the software.