When a wiki page is renamed or deleted, the counters used by the PageViewPlugin (http://www.jspwiki.org/wiki/PageViewPlugin) are not adapted accordingly. As a results of this, the overview of counters can contains pages that do not exist anymore. The counters of these pages will not be incremented anymore, so they will disappear of the top list, but they still remain in the full list. It would make sense to remove the counters for deleted pages. It would defnitely make sense to update the counters when a page is renamed.
A visit to a non existing page is also stored by the PageViewPlugin, eg by clicking on a link to a page showing the message "This page does not exist. Why don't you go and create it?" is stored as a valid visit. Counting visits to non existing pages seems something of very low value.