How do I delete the mail that has been saved to Archives? Why does it save to an Archive and not just be deleted, anyway?
Apple has made archiving by default as when users realizes that they have deleted an important message,they can quickly restore it without much searching.
Now,to delete messages -
As described in the above site , (applies only to Gmail and Google Apps accounts)
Go to Settings --> Mail --> Contacts --> Calendars --> email account.
Turn off the Archived Messages option and now all your deleted messages will go to Trash.
Screenshot - http://img.labnol.org/files/delete-archive.jpg