Well, consider this: I, as many others, use different identities for different purposes. So most likely, if you search for me, you will NOT find a major part of my forum posts if I only give you my name, educational and professional history.
If sb isn't communicating, it tells me exactly that. If the internet and business networking is an important part of his/her potential job, it would make a negative impression if the person doesn't even have a linkedin/xing/etc. profile. Don't try to link things that are obviously unconnected, like experience and online presence.