Unfortunately the nested views do not work as described in custom directives. This behavior seems to have changed with the release of 0.2.8. You can easily test this here:
http://plnkr.co/edit/ZrM9TFhrIMe1dtkRu7K3?p=preview
If you like to test the same script with 0.2.7, simply change the source of the script in the index.html from "angular-ui-router.0.2.8.js" to "angular-ui-router.0.2.7.js" and voilà it is working.