re: polite rebuke
This is often done here, and is not intended as any kind of rebuke. One assumes if the original post doesn't have a link, that either it is a secondary reference (like a short newspaper item) that may not have linked to the original source, or sometimes because the person isn't that familiar with the linking process. Finding the original and adding a link is just kind of an assist.
Matt Drudge posted a quote from Bob Novak without mentioning the original source. Had someone else quoted Drudge's item in a post, I probably would have tacked on the original source link if I found it.