This is a quick tutorial on how to customize links and tabs on pages gadget, in case you want to have a tab to link to some other URL instead of your static pages alone (how selfish the current limitation is!). Do note that after this hack, you won't be able to edit your pages gadget directly by clicking on 'Edit' on your Pages Gadget from Page Element. You'd have to code it each time you wanna make changes. So if you have added a new static page, it wont automatically show on your Pages Gadget unless you make the necessary changes.
Make sure you have already added your Pages Gadget before attempting this tutorial.
Update: With the new Blogger interface, you can add external links to your Pages gadget.