I have received a few requests to delete accounts. The general rule is no, accounts are not deleted unless there is a valid reason.
The main reason for this policy is that it is more administrative work. I have had some people request deletion because of some emotional issue, then change their mind later. I have not seen this but a mod brought up this scenario - it is possilble someone may get on someone's computer and pretend to be that person and request deletion of the account as a joke or out of malice. Deleting is not something that can be reversed.
Also, once things start getting deleted, threads may become confusing because context is lost.