When there are zero watchers on an issue, the number "0" is a link to the "Manage Watchers" page.
When there are zero voters on an issue, the number "0" is not a link to the "Manage Voters" page.

However, if the current user is the only voter on the issue and removes his/her vote, the number of voters changes to "0" but remains a link.

Since the text "Votes" remains a link at all times, for consistency it would make sense for the number to remain a link as well.