How could you possibly suggest that those doing this are doing it out of a secret 
  need to build their public profile. That's a pretty cynical worldview.

I think it is a valid concern. I don't say for all of the 'Offer HN' threads but some of the them just don't sound right. (I would be the first one to admit, I am not the best when it comes accurately judging intentions from just a couple of written lines.)

Case in example - http://news.ycombinator.com/item?id=1839507

Sorry if I misunderstood this poster, but from a genuine offer to help in one thread, it quickly went to offering of services here. (I hope the person corrects me if that really isn't the case.)