Issue: Feture or bug?

This is intentional, since wiki posts don't really "belong" to anyone. Many people can edit a post, which would make the number of people who can't rate the post especially high. After each edit, the article can change significantly enough that it's effectively not even the article that was originally posted. In this case, it's no longer fair to prevent the creator from rating the article (nor subsequent editors) - but then these people can modify it to make it "theirs" in the future.

There's no good way to automate such a subjective feature which calculates the user's ability to rate based on the quality of the post related to the quality of subsequent edits - and revokes their ratings later on. The only effective way of controlling this is to limit the users who can rate to those who can't modify it to begin with - but this also limits one of the many already underused features of vBulletin, so we just don't do it.

As you can see we've given a lot of thought to this, so you can consider the current state a "feature".