That's normal because of the development cycle. They will change to 13.04 once the final release arrives. I would also recommend making sure all repositories are activated in the Software & Updates app (Found in Dash):
NOTE - Since this is a development version, you will sometimes get when doing an update an error. Maybe it will say "Bad checksum", maybe "Repository not available" or maybe other errors related to repositories. Do not worry about this. Simply wait a while, I normally wait an hour before doing the update process again. It happens a lot on Development versions before they are released. A lot of repositories are updated on a daily basis. So the whole update system might show an error while you do the update.