I receive several link removal requests a month from people who have left legitimate comments on my blogs. These people followed the rules and only embedded links in the little URL field that WordPress provides by default in the comment form. It is not required that you place a link there but most people do it.
The links use the “rel=’nofollow’” attribute and I manually review all the comments. Once in a blue moon a spammer gets past my vigilance with a well-crafted generic comment. I have learned to be more suspicious and to sometimes search the Web for the 1-2 sentences that the spammers leave before approving comments.
The Problem Is Not the Links: It is the Lack of Research