Thus, anonymity is no excuse for not heeding a person's concerns -- in fact, in the real world, some of the best tips received by law enforcement, tax administration, SEC violations, etc., are anonymous. As KC noted earlier, it is the content that matters not the source, and in this case the content is valid.
When someone anonymously reports a crime, they are reporting a verifiable fact (if the appropriate authorities cannot verify it, they won't do anything about it). The Concerned Wikipedian's email did not contain facts, it contained opinions (any facts stated were already known to anyone following the case). Therefore, it is not comparable to an anonymous tip off.