I believe you made my point for me, it isn't the equivalent of reaching out as the person will never see it. Sure you might want that person to know you care but given they never will know as they will never see it, it is an exercise in futility.
I don't see how you are showing empathy or caring when the person on the receiving side never knows or benefits from it. It isn't the same as donating to a telethon for a hurricane or flood victim where there might actually be a benefit to the victims at the end of the day. They are anonymous and the person receiving the benefit will never know who sent it, but at least they get a benefit. Both sides feel better, the person for giving the $$ and the one receiving it.
A condolence thread on a webboard that will just sit there and never be seen to me is a meaningless gesture to the victim.