I suspect the real reason is that they have policies they must follow, even when it's counterproductive, because so few of the editors are knowledgable enough to make an informed decision. There is a danger of wikipedia becoming a tool for self-promotional fluff, for example see Technical Analysis Software which is constantly being spammed by vendors of TA software. To avoid this, a policy of not allowing links to your own content makes a bit of sense. There's nothing to stop someone else linking to it - oops, I just did. Let's see if they block me from editing.