It'd be my guess that your user name forms the primary key for users in the RR DB. If that is the case - and assuming RI is enforced - once you've created an account it couldn't easily be removed (might have forum post refs, gallery uploads and marketplace purchases associated with it, among many other things) and although all of these things could be removed I assume that RR choose not to do so. It is probably safer all around to just abandon your account and start anew. I may be wide of the mark and no slight is intended to RR's system policies in this, I can think of many reasons why they wouldn't want to allow deletion of an account, but is it possible to make an account "inactive" (i.e. incapable of further login) though?